Layered Heterostructured Composite Comprising Nickel-Iron Hydroxide and Ceramic, Electrocatalyst for Water Electrolysis Comprising the Same, and Method for Preparing the Same

Abstract

The present invention relates to a layered heterostructure catalyst for oxygen evolution reaction (OER), wherein a nickel-iron layered double hydroxide (NiFe-LDH) layer is electrodeposited on a carbon cloth substrate, and a ceramic layer is formed thereon. Through an optimal layer sequence arrangement in which NiFe-LDH acts as the substrate contact layer and the ceramic acts as the surface active layer, a low overpotential of 493 mV, a Tafel slope of 79.3 mV / dec, and a charge transfer resistance of 1.35 Ω·cm2 are achieved at 300 mA / cm2. This represents a performance improvement of 167 mV (25.3%) compared to pure NiFe-LDH and 93 mV compared to an inverse sequence structure, proving that the layer sequence is a key design parameter for catalyst performance. Significant cost reductions are achieved compared to precious metal catalysts by using only index-abundant elements, and the catalyst exhibits over 90% durability during 20 hours of continuous operation, making it applicable to alkaline water electrolyzers for green hydrogen production.

Description

Technology Field

[0001] The present invention relates to a layered heterostructured composite comprising a layered heterostructured nickel-iron hydroxide (NiFe-LDH) and a ceramic, an electrode catalyst for water electrolysis comprising the same, and a method for manufacturing the same, and in particular, to a layered heterostructured catalyst for an oxygen evolution reaction (OER), a water splitting device (SPD) comprising the same, and a method for manufacturing the same. Specifically, the present invention relates to a novel layered heterostructured oxygen evolution reaction (OER) catalyst formed by sequentially depositing a nickel-iron layered heterostructured hydroxide (NiFe-LDH) and a ceramic on a conductive carbon cloth substrate. Background Technology

[0002] Efforts to explore sustainable, clean, and efficient energy generation to meet the energy demands of modern society are ceaseless. Water electrolysis is a promising method for producing hydrogen, a clean energy source. Water electrolysis using electrode catalysts uses electricity to decompose water into hydrogen and oxygen at the cathode and anode, respectively. These are called the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER), respectively.

[0003] Electrode catalysts for OER are a critical component of many cutting-edge technologies. However, the slow reaction rate of OER significantly hinders the practical application of these technologies, creating a need for the development of feasible, stable, and inexpensive catalyst systems.

[0004] Oxygen evolution catalysts used in modern water splitting systems rely primarily on platinum group metal (PGM) oxides, specifically iridium dioxide (IrO2) and ruthenium dioxide (RuO2), which serve as the standard benchmark for OER catalysts in both acidic and alkaline media. Iridium dioxide exhibits an OER of 10 mA / cm² under alkaline conditions. 2 It exhibits excellent activity with a low overpotential of 270 mV and a Tafel gradient of 40–50 mV / dec, making it the preferred material for anodes in commercial proton exchange membrane (PEM) water electrolyzers. Ruthenium dioxide offers a cost advantage of being one-eighth the price of iridium, while also providing 10 mA / cm² depending on the form and synthesis route. 2 It exhibits excellent OER dynamics with an overvoltage of approximately 250-325 mV.

[0005] However, these precious metal catalysts have fatal practical limitations that fundamentally hinder the deployment of gigawatt-scale hydrogen production infrastructure needed for global energy decarbonization. The biggest limitation is severe resource scarcity. Global iridium production is only sufficient to supply a tiny fraction of the electrolyzer capacity required for the hydrogen economy, and less than 5% of annual iridium production can be allocated to water splitting applications, creating an insurmountable bottleneck for large-scale deployments.

[0006] In response to the limitations of platinum group metals, extensive research has focused on the development of ground-abundant non-precious metal catalysts, and nickel-iron layered double hydroxide (NiFe-LDH) has emerged as the most promising non-precious metal alternative for alkali OER catalysts. Pure NiFe-LDH [achieves] academic benchmark conditions (10 mA / cm² 2 It exhibits decent performance with an overvoltage of 220-294 mV and a Tafel slope of 36-103 mV / dec. However, the critical limitations of pure NiFe-LDH become clear when evaluated at industrially effective current densities.

[0007] The academic test standard is 10 mA / cm2 While an acceptable overpotential is achieved, the overpotential of the same catalyst rises sharply at high current densities. NiFe-LDH at 100 mA / cm² in an alkaline medium 2 At 260-300 mV, 500 mA / cm 2 At this point, it soars to 476–503 mV. This dramatic increase in overpotential reflects two fundamental kinetic limitations: (i) slow electron transport kinetics due to low electrical conductivity at the electrode-electrolyte interface, and (ii) the lack of density and accessibility of catalytic active sites, which become the rate-determining step under high current conditions.

[0008] The Tafel slope of pure NiFe-LDH, which is often reported to exceed 80 mV / dec at high current densities, indicates that the rate-determining step of oxygen evolution is energetically unfavorable, suggesting that despite the low current density performance of NiFe-LDH, the oxygen intermediate stabilization and water dissociation kinetics are still poor.

[0009] Recently, studies have been conducted on heterogeneous composite structures combining NiFe-LDH with secondary catalytic phases such as MoS2, metal phosphides, and various metal-organic frameworks (MOFs). A notable example is the NiFe-LDH / MoS2 composite, which exhibits an impressive Tafel gradient of 43 mV / dec and an alkaline electrolyte of 400 mA / cm². 2 An overpotential of 407 mV was achieved. Although there has been a substantial performance improvement, the composite approach introduces new limitations: (i) the addition of secondary phases increases material costs and manufacturing complexity, partially offsetting the cost advantages of non-precious metal catalysts; (ii) the fabrication of NiFe-LDH / MoS2 and similar composites requires precise control of interfacial quality and phase distribution, limiting industrial scale-up; and (iii) the understanding of the mechanism of synergy is incomplete and often conflicts across the literature.

[0010] Above all, existing heterostructure studies have focused solely on changes in the support (carbon cloth, nickel foam, etc.) or the integration of secondary phases, and have not systematically explored the impact of layer-sequence positioning—that is, the order and spatial arrangement of different catalytic phases—on overall performance. This critical design parameter has been overlooked in all previous composite catalyst studies.

[0011] A chronic problem with OER catalyst literature is the low current density test (10-100 mA / cm²). 2 By using ) as the primary performance indicator to make the catalyst performance appear acceptable, while under actual industrial operating conditions (200-500 mA / cm²) 2 It masks the fundamental dynamic limitations that are revealed only in ). In addition, charge transfer resistance (R ct Indicators that provide mechanistic insights into performance limits, such as electrochemical active surface area (ECSA) and exchange current density (j0), are reported inconsistently across studies, making direct comparison and rational design very difficult.

[0012] A fundamental weakness of existing composite OER catalysts is the absence of rational design principles defining their heterostructure configurations and architectures. Most composite catalysts are developed through the empirical screening of random phase combinations, without systematic investigation into why specific configurations are superior to others. Due to a lack of understanding regarding the roles of electronic metal-support interactions (EMSI), interfacial charge distributions, and heterointerfacial electronic structures, it is impossible to rationally predict combinations that produce synergistic effects as well as those that produce antagonistic effects by blocking active sites. This mechanistic gap explains why the development of composite catalysts has stagnated despite decades of research. Prior art literature

[0013] 1. Korean Registered Patent No. 10-1733492 2. Korean Registered Patent No. 10-0785043 3. Korean Published Patent No. 10-2023-0030188

[0014] 1. Chemistry of Materials (2024), 36(1), 275-285 The problem to be solved

[0015] The present invention aims to solve the technical problems of the existing technology described above, provide a layered heterostructure composite that can be utilized as an electrode catalyst for water electrolysis with excellent performance, and a water electrolysis device including the same, thereby achieving green hydrogen production by water electrolysis.

[0016] The main objectives of the present invention are as follows:

[0017] (i) Low overpotential (300 mA / cm²) suitable for commercial alkaline water electrolyzers 2 Developing an oxygen evolution reaction catalyst that achieves excellent kinetics at less than 500 mV;

[0018] (ii) to systematically explore various spatial arrangements of NiFe-LDH and ceramic layers, and to discover an optimal heterostructure in which NiFe-LDH acts as the substrate contact layer and the ceramic acts as the surface active layer, thereby overcoming the performance limitations of pure NiFe-LDH catalysts and achieving excellent electron transfer and oxygen evolution kinetics;

[0019] (iii) demonstrating that the catalyst layer position is an important and non-trivial design parameter for heterostructure optimization through systematic layer sequence changes, and providing rational design principles for future multilayer catalyst systems;

[0020] (iv) Eliminating dependence on rare platinum group metals and utilizing indicator-rich, non-toxic elements that enable mass production at low cost;

[0021] (v) Enabling low-cost, high-efficiency electrochemical hydrogen production compatible with renewable energy integration. means of solving the problem

[0022] The present invention relates to a layered heterostructure composite comprising (a) a substrate, (b) a substrate contact layer located on the substrate and comprising a nickel-iron layered double hydroxide (NiFe-LDH), and (c) a surface active layer located on the substrate contact layer and comprising a ceramic, wherein the ceramic nanoparticles are represented by the following chemical formula.

[0023] [Chemical Formula 1]

[0024] Pb 10-x Cu x [(PO4) 6-y (SO4) y ]O z S z'

[0025] x is a real number between 0.9 and 9.9, and y is 10 -10 It is a real number from 5.9 to 10, where z and z' are each 10 -10 It is a real number between 4 and 10, and z+z' is 10 -10 It is a mistake of up to 4.

[0026] In this specification, 'ceramic' means a substance represented by Chemical Formula 1 unless otherwise specified.

[0027] Another aspect of the present invention relates to an electrode catalyst comprising a layered heterostructure composite according to various embodiments of the present invention.

[0028] Another aspect of the present invention relates to an electrode for water electrolysis comprising a layered heterostructure composite according to various embodiments of the present invention.

[0029] Another aspect of the present invention relates to a water electrolysis device comprising a layered heterostructure composite according to various embodiments of the present invention.

[0030] Another aspect of the present invention relates to a method for manufacturing a layered heterostructure composite comprising (A) forming a NiFe-LDH layer on a substrate through electrodeposition, and (B) forming a ceramic layer on the NiFe-LDH layer by vacuum thermal evaporation deposition of ball-milled ceramic powder, wherein the ceramic is represented by the chemical formula 1. Effects of the invention

[0031] According to various embodiments of the present invention, the technical problems of the existing technology described above are resolved, and a layered heterostructure composite for an electrode catalyst having excellent OER performance, an OER electrode catalyst including the same, a water electrolysis device including the same, and a method for manufacturing the same are provided, and ultimately, green hydrogen production through water electrolysis can be achieved through the same.

[0032] The S4 heterostructure of the present invention is 300 mA / cm 2 It exhibits an oxygen evolution overpotential of 493 mV, which signifies a performance improvement of 167 mV (25.3%) compared to pure NiFe-LDH (S2: 660 mV) and 466 mV (48.6%) compared to bare carbon cloth (S1: 959 mV). This corresponds to 300 mA / cm² 2 By lowering the electrolytic cell voltage by about 170 mV, it improves electrical energy efficiency by 5-8% and enables hydrogen production costs that meet the U.S. Department of Energy (DOE) Hydrogen Shot goal of achieving $1 / kg H2 by 2031.

[0033] The main advantages and effects of the present invention compared with conventional technology are as follows:

[0034] (1) Non-obviousness of systematic optimization: By showing that the S4 structure (LDH base / ceramic surface) has 93 mV better performance than the inverse structure S3 (ceramic base / LDH surface, 586 mV), it was established that the layer position is a key parameter in determining performance. S4 achieves an optimal balance between electron transfer (substrate contact LDH) and OER catalysis (surface ceramic).

[0035] (2) Excellent dynamics and surface area: S4 has a low Tafel slope of 79.3 mV / dec and 1.35 Ω·cm 2 Low charge transfer resistance (75.3% reduction compared to bare CC), and the highest among all variants at 304.5 cm 2 Represents the ECSA of.

[0036] (3) Robust durability: 300 mA / cm 2 Durability suitable for commercial deployment was confirmed by demonstrating an active retention rate of over 90% during 20 hours of continuous operation at high current density.

[0037] (4) Significant cost reduction: Material costs were reduced to about $50 / kg by using surface-abundant elements (Ni, Fe, Cu, Pb, P). This represents a 120-fold cost reduction compared to RuO2 ($6,000 / kg) and a 1,000-fold reduction compared to IrO2 ($50,000 / kg), completely eliminating dependence on iridium, which is subject to supply chain constraints.

[0038] (5) Mechanism identification: A binding energy shift of 0.1-0.3 eV via XPS analysis (confirmed by EMSI) and the identification of sharp heterointerfaces and lattice defects of 1-5 nm via HRTEM demonstrate the cause of catalytic synergy beyond simple material mixing.

[0039] (6) Energy and economic impact: 300 mA / cm 2Based on a 1 MW electrolyzer in operation, a voltage reduction of 170 mV reduces input power by 40 kW and realizes an annual energy saving of 350 MWh (approximately $35,000 per year at $100 / MWh). At the global target scale of 10 GW hydrogen production, an annual energy saving of 3.5 GWh is possible. Brief explanation of the drawing

[0040] Figure 1 shows a detailed experimental process schematic (electrodeposition and thermal evaporation steps) of the ceramic / NiFe-LDH OER catalyst. Figure 2 shows the electrochemical activity data of the fabricated material: (a) LSV polarization curve, (b) Tafel slope value, (c) EIS Nyquist plot, (d) CV curve for Cdl measurement, (e) Cdl value for ECSA measurement, (f) overvoltage comparison at various current densities. Figure 3 shows the Raman spectra of electrodes S2 to S4. Figures 4a to 4e show the XPS spectra of electrodes S2 and S4, respectively. Figures 4a to 4c are high-resolution XPS spectra of the Ni 2p, Fe 2p, and O 1s regions of the NiFe-LDH electrode and the ceramic-coated NiFe-LDH (S4) electrode, showing the chemical states of Ni, Fe, and O species before and after ceramic modification. Figures 4d and 4e are XPS spectra of the Cu 2p and Pb 4f regions detected only in the ceramic-coated NiFe-LDH electrode, showing that ceramic components were successfully introduced onto the NiFe-LDH surface. Figures 5a to 5f are scanning electron microscope (SEM) images of the S2 electrode, respectively. Figure 6 shows TEM and HRTEM images of the S4 electrode, illustrating the heterogeneous interface structure. Specific details for implementing the invention

[0041] Below, various aspects and embodiments of the present invention will be examined in more detail.

[0042] Expressions such as 'comprising,' 'having,' 'consisting of,' and 'composed of' in this specification may have additional parts added unless 'only' is used. Furthermore, numerical values ​​or numerical ranges described in this specification are interpreted to include a margin of error unless otherwise explicitly stated. Additionally, expressions 'X to Y' indicating a numerical range in this specification mean 'X or greater and Y or less.'

[0043] Embodiments of the present invention will be described in detail below with reference to the drawings. However, detailed descriptions of known functions or configurations that may obscure the essence of the present invention in the following description and the attached drawings are omitted. Additionally, throughout the specification, the term 'comprising' a component means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0044] Unless specifically defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0045] One aspect of the present invention relates to ceramic nanoparticles for electrode catalysts represented by the above chemical formula 1.

[0046] According to various aspects and embodiments of the present invention, the above ceramic may be used as a composite with nickel-iron layered double hydroxide (NiFe-LDH) to be utilized as an electrode catalyst, particularly for an oxygen evolution reaction (OER); as a water electrolysis device including the same; and as various other multifunctional materials.

[0047] If some of the components constituting the ceramic are omitted or fall outside the compositional range, it is undesirable in that the effects according to various aspects and embodiments of the present invention cannot be fully expressed.

[0048] In particular, if some of the components constituting the ceramic are omitted or fall outside the compositional range, the improvement in electrical conductivity is not effective, unlike the ceramic of the composition according to the present invention, and thus the synergistic effect between NiFe-LDH and the ceramic may not be observed.

[0049] According to one embodiment, x in Chemical Formula 1 is 2.1 to 9.9. Increasing the amount of Cu doping is desirable because it changes the band energy of the ceramic of Chemical Formula 1, thereby significantly improving conductivity. However, if it deviates from the upper and lower limits, it is not desirable because the effect of improving conductivity or the effect of improving the electrochemical performance of the composite electrode containing it is negligible.

[0050] In particular, when x is 2.1 or higher, a binding energy shift of 0.1-0.3 eV in the Ni 2p and Fe 2p peaks is observed in XPS analysis, confirming the manifestation of electronic metal-support interaction (EMSI), whereas when x is less than 2.1, the said binding energy shift is not observed. The effect of improved OER performance due to the manifestation of EMSI is a heterogeneous effect in which the manifestation differs at the boundary of x = 2.1, and it appears to be because when the amount of Cu doping reaches the critical value (x = 2.1), the electronic structure of the ceramic changes rapidly, enabling efficient charge transfer at the interface with NiFe-LDH.

[0051] Another aspect of the present invention relates to a layered heterostructure composite comprising (a) a substrate, (b) a substrate contact layer located on the substrate and comprising a nickel-iron layered double hydroxide (NiFe-LDH), and (c) a surface active layer located on the substrate contact layer and comprising a ceramic of Formula 1.

[0052] According to one embodiment, the invention may relate to a layered heterostructure composite comprising (a) a carbon cloth substrate, (b) a nickel-iron layered double hydroxide (NiFe-LDH) nanostructure formed by electrodeposition on the substrate, and (c) a plurality of ceramic nanoparticles positioned on the surface of the nanostructure by thermal evaporation deposition.

[0053] The layered heterostructure composite of the present invention is characterized by a specific layer sequence in which NiFe-LDH functions as a substrate-contacting layer and ceramic functions as a surface-exposed layer. This layer sequence, discovered through systematic experiments in the present invention, exhibits significantly superior OER catalytic performance compared to the reverse arrangement (NiFe-LDH surface / ceramic base).

[0054] The difference in OER performance according to this layer sequence exhibits heterogeneous effects that go beyond mere quantitative differences. Specifically, in the S4 structure, where NiFe-LDH is the substrate contact layer and the ceramic is the surface active layer, efficient electron transfer from the substrate through NiFe-LDH and optimized OER catalytic activity on the ceramic surface are achieved simultaneously. In contrast, in the reverse order S3 structure, the ceramic layer is located between the substrate and NiFe-LDH, causing a bottleneck in the electron transfer pathway. Since these heterogeneous effects vary depending on the layer sequence, it implies that even when the same components are used, synergistic effects by EMSI are not manifested if the layer sequence is reversed.

[0055] According to another embodiment, the layered heterostructure composite has 300 mA / cm² 2 It exhibits an oxygen evolution overpotential of approximately 493 mV.

[0056] According to another embodiment, the layered heterostructure composite exhibits an overpotential 93 mV lower than the NiFe-LDH / ceramic layer sequence (S3) in which the ceramic / NiFe-LDH layer sequence (S4) is reversed. This demonstrates that the layer position is an important and non-obvious design parameter that determines the OER performance of the heterostructure catalyst.

[0057] The material of the electrode substrate used in electrochemical water splitting (OER or HER) can have a significant effect on the electrochemical behavior of the electrode catalyst formed thereon. Examples of materials that can be used as a substrate in the present invention may include, but are not limited to, one or more selected from carbon cloth, nickel foam, copper foam, graphite paper, carbon fiber paper, stainless steel mesh, and titanium mesh.

[0058] In the present invention, carbon cloth is the most preferred substrate material among the above-mentioned materials. Using carbon cloth is most preferable because, unlike when using other substrate materials mentioned above, it is possible to grow NiFe-LDH nanostructures on the surface of the substrate and deposit multiple ceramic nanoparticles with a uniform distribution thereon without using a binder (such as Nafion, PTFE, or PVDF).

[0059] According to another embodiment, the carbon cloth substrate has a geometric area of ​​1-100 cm² 2 am.

[0060] According to another embodiment, the above x is 2.1-9.9.

[0061] According to another embodiment, in the above chemical formula 1, x is 2.1 to 9.9.

[0062] In the range where x is between 0.9 and 9.9, the electrical conductivity of the ceramic is enhanced by Cu doping, resulting in superior OER performance in the composite with NiFe-LDH compared to pure NiFe-LDH. In particular, when x is 2.1 or higher, a binding energy shift of 0.1–0.3 eV in the Ni 2p and Fe 2p peaks is observed in XPS analysis, confirming the manifestation of electronic metal-support interactions (EMSI); conversely, when x is less than 2.1, the aforementioned binding energy shift is not observed. Since superior OER performance can be achieved when x is 2.1 or higher due to this EMSI manifestation, it is more desirable.

[0063] According to another embodiment, the carbon cloth substrate is pretreated by sequentially ultrasonically cleaning with HCl, KOH, and deionized water before electrodeposition.

[0064] In various aspects of the present invention, according to one embodiment, the NiFe-LDH nanostructure is formed on the carbon cloth substrate by electrodeposition.

[0065] The above NiFe-LDH nanostructures are in the form of multiple nanosheets or nanoplatelets. The longitudinal thickness of the nanostructures is 15-30 nm, and the lateral dimension is 100-300 nm.

[0066] According to another embodiment, the plurality of NiFe-LDH nanosheets are each structurally connected to adjacent nanosheets to form a hierarchical nanostructure.

[0067] According to another embodiment, the plurality of NiFe-LDH nanosheets are formed in a random orientation on the fiber surface of the carbon cloth substrate, thereby providing an enhanced surface area.

[0068] Specifically, the plurality of nanosheets are each structurally connected to adjacent nanosheets to form a hierarchical nanostructure, and it is preferable that at least 60% of the plurality of nanosheets are formed in a random orientation on the surface of the substrate.

[0069] In various aspects of the present invention, according to one embodiment, the plurality of ceramic nanoparticles are positioned on the surface of the NiFe-LDH nanostructure by thermal evaporation deposition.

[0070] According to another embodiment, the plurality of ceramic nanoparticles are positioned on the surface of the NiFe-LDH nanosheet as a conformal or partially conformal coating.

[0071] According to another embodiment, the thickness of the ceramic coating is 5-20 nm, preferably 10-15 nm.

[0072] According to another embodiment, the plurality of ceramic nanoparticles are a unit area (cm²) of the substrate. 2It is included in an amount of 1-10 mg based on ).

[0073] In various aspects of the present invention, according to one embodiment, the layered heterostructure composite forms a tight heterointerface between NiFe-LDH and the ceramic.

[0074] According to TEM analysis, the heterogeneous interface region exhibits the following characteristics:

[0075] (i) The presence of visible misfit dislocations and edge dislocations in the range of approximately 1–5 nm across the heterogeneous interface confirmed the presence of interfacial strain;

[0076] (ii) Point defects, oxygen vacancies, and potential short-range order variations exist at the heterogeneous interface and function as catalytic active sites;

[0077] (iii) A sharp interface is exhibited in most areas between the NiFe-LDH and the ceramic phase through atomic resolution contrast, indicating good heterogeneous interface contact;

[0078] (iv) Direct contact between the two crystal phases without a significant amorphous interface region ensures efficient electron transfer.

[0079] According to another embodiment, the layered heterostructure composite exhibits a fine binding energy shift of 0.1-0.3 eV at the Ni2p and Fe2p peak positions relative to pure NiFe-LDH in XPS analysis, which indicates electron redistribution and electronic metal-support interaction (EMSI) occurring at the heterostructure interface.

[0080] In various aspects of the present invention, according to one embodiment, the layered heterostructure composite exhibits both the characteristic vibration band of NiFe-LDH and the characteristic vibration band of the ceramic in Raman spectroscopy analysis.

[0081] Specifically, pure NiFe-LDH / CC(S2) is 460-480 cm -1 (Fe 3+ / Ni 2+ -O-Ni 2+ and Fe 3+ -O-Fe 3+ Metal-oxygen stretching vibration), 515-560 cm -1 (MO stretching vibration, M = Ni or Fe), and 640-730 cm -1 It shows characteristic vibrational bands in (symmetric stretching of Ni-O and Fe-O bonds and Ni-O-Fe cross-linking interactions).

[0082] In the composite electrodes (S2, S4), all NiFe-LDH characteristic bands were retained, confirming the structural integrity of the LDH phase during composite formation. Importantly, a new Raman band at 200–500 cm⁻¹, attributed to vibrational modes of the ceramic secondary phase, was observed. -1 and 600-900 cm -1 It appeared in the region, which is Cu-O stretching (~400-500 cm -1 ), PO expansion (~600-700 cm) -1 ), and Pb-O expansion (~400-600 cm -1 Includes ).

[0083] According to another embodiment, NiFe-LDH MO stretching band (460-480 cm -1 and 515-560 cm -1 The relative intensity ratio of ) shows a slight change (3-8% variation) in the composite electrode compared to pure S2, which is consistent with the electronic metal-support interaction (EMSI) at the heterointerface where electron density is redistributed between NiFe-LDH and the ceramic phase.

[0084] In various aspects of the present invention, according to one embodiment, the layered heterostructure composite exhibits the following characteristics in X-ray photoelectron spectroscopy (XPS) analysis.

[0085] The Ni2p region of NiFe-LDH (S2) contains Ni within the LDH structure at a binding energy of 857.6 eV. 2+ It exhibits a characteristic major peak and shows minor satellite splitting at a binding energy approximately 6 eV higher, Ni 2+ Check the oxidation state. The Fe2p region is Fe, the major iron oxidation state of NiFe-LDH. 3+ It exhibits a dominant peak at 712.0 eV, corresponding to.

[0086] The O1s region is deconvolved into two major components: (i) metal-bonded oxygen (MO) at approximately 528.9 eV representing lattice oxygen within the LDH framework, and (ii) hydroxyl oxygen (OH) at approximately 532.3 eV representing structural and surface hydroxyl groups.

[0087] New photoelectronic signals from copper and lead species appeared at the composite electrode: Cu2p at 932.8 eV (Cu + ) and 934.8 eV(Cu 2+ It shows a major contribution at ) and exhibits a ~8 eV separated characteristic shakeup satellite peak, confirming the presence of mixed valence copper species within the ceramic phase. Pb4f7 / 2 is Pb in the lead-containing phase. 2+ or Pb 4+ It appeared at 137.8–138.6 eV, corresponding to the species. P2p was detected at 133–135 eV, consistent with phosphorus in phosphide coordination.

[0088] In various aspects of the present invention, according to one embodiment, the layered heterostructure composite exhibits the following electrochemical properties.

[0089] The above complex produces 300 mA / cm² in a 1 M KOH aqueous alkaline electrolyte. 2It exhibits an oxygen evolution overpotential of approximately 493 mV relative to RHE at a current density.

[0090] According to another embodiment, the composite exhibits a Tafel slope of 79.3 mV / dec, which indicates fast electrochemical kinetics and favorable oxygen intermediate stabilization on the catalyst surface.

[0091] According to another embodiment, the composite is 1.35 Ω·cm 2 The charge transfer resistance (R ct It represents ), which is a value reduced by 75.3% compared to bare carbon cloth.

[0092] According to another embodiment, the composite exhibits an electrochemically active surface area (ECSA) of 304.5 cm2, which is the highest value among all layer sequence variants, indicating excellent electron transfer efficiency and abundant and accessible catalytic active sites.

[0093] One of the key technical features of the present invention is the discovery that the layer sequence of NiFe-LDH and ceramic has a decisive influence on OER catalyst performance.

[0094] In the present invention, various layer sequence variants as follows were systematically prepared and evaluated:

[0095] - S1: Bare Carbon Cloth (CC)

[0096] - S2: NiFe-LDH / CC with only NiFe-LDH electrodeposited

[0097] - S3: NiFe-LDH / Ceramic / CC (reverse order) with ceramic deposited first followed by NiFe-LDH electrodeposited

[0098] - S4: Ceramic / NiFe-LDH / CC in which NiFe-LDH is first electrodeposited and then ceramic is deposited (optimal structure of the present invention)

[0099] - S5: NiFe-LDH / ceramic / NiFe-LDH / CC trilayer structure

[0100] As a result of evaluation through the above systematic variations (S2, S3, S4, S5), as shown in Table 1 below, the ceramic / NiFe-LDH sequence (S4: 493 mV) showed 93 mV better performance than the reverse sequence NiFe-LDH / ceramic sequence (S3: 586 mV), establishing that the layer position is an important and non-trivial design parameter.

[0101] The S4 configuration achieves an optimal balance between electron transfer (substrate contact NiFe-LDH) and oxygen evolution catalysis (surface ceramic), whereas the reverse order of S3 causes an interfacial conductivity bottleneck. These results are significant in that the layer sequence position is an important design parameter for heterostructure optimization and provides rational design principles for future multilayer catalyst systems.

[0102] Another aspect of the present invention relates to an electrode catalyst comprising a layered heterostructure composite according to various embodiments of the present invention.

[0103] According to one embodiment, the electrode catalyst is for an oxygen evolution reaction (OER).

[0104] According to another embodiment, the electrode catalyst is used as an anode catalyst for an alkaline water electrolyzer.

[0105] Another aspect of the present invention relates to an electrode for a water electrolysis device comprising a composite according to various embodiments of the present invention.

[0106] According to one embodiment, the electrode for water electrolysis is for an oxygen generation reaction.

[0107] According to another embodiment, the electrode for water electrolysis is uniformly deposited on a carbon cloth without a binder such as Nafion, PTFE, or PVDF.

[0108] According to another embodiment, the catalyst loading amount of the electrode for water electrolysis is 1-10 mg / cm²2 am.

[0109] Another aspect of the present invention relates to a water splitting device (SPD) comprising (i) a working electrode, (ii) a counter electrode, and (iii) a reference electrode, wherein the working electrode is an electrode for water electrolysis according to various embodiments of the present invention.

[0110] According to one embodiment, the water electrolysis device is an alkaline water electrolyzer (AWE).

[0111] According to another embodiment, the water electrolysis device comprises (a) a reaction chamber containing a 1 M KOH electrolyte; and (b) an anode containing a ceramic / NiFe-LDH catalyst on a carbon cloth (1-10 mg / cm²). 2 (Loading); (c) cathode for hydrogen evolution reaction; (d) hydroxide exchange membrane; and (e) 200 mA / cm² 2 The above includes a power supply (1.8-2.5 V) for operation.

[0112] According to another embodiment, the water electrolysis device has an amperage of 200-500 mA / cm² 2 Operating with a Faraday efficiency exceeding 95%, and 300 mA / cm² relative to a pure NiFe-LDH anode 2 Achieve a cell voltage reduced by more than 100 mV.

[0113] According to another embodiment, the ceramic / NiFe-LDH anode in the water electrolysis device has a current of 300 mA / cm² 2 It maintains more than 90% activity during 20 hours of continuous operation.

[0114] According to another embodiment, hydrogen produced by the water electrolysis device is utilized in hydrogen fuel cell vehicles, green ammonia synthesis, green methanol production, grid-scale energy storage, or industrial process heat applications.

[0115] According to a preferred embodiment, the electrode catalyst according to various embodiments of the present invention is binder-free, such as Nafion, PTFE, and PVDF, 1-100 cm 2 It can be uniformly deposited on a carbon cloth of a certain area and can be applied to an anode catalyst for OER in an alkaline water electrolysis device adopting an alkaline electrolyte.

[0116] The water electrolysis device of the present invention as described above has an amperage of 200-500 mA / cm² 2 It operates with a Faraday efficiency of over 95% at a current density of , and 300 mA / cm² compared to a pure NiFe-LDH anode. 2 It can achieve the effect of reducing the cell voltage by more than 100 mV.

[0117] Another aspect of the present invention relates to a method for manufacturing a layered heterostructure composite comprising the steps of: (A) forming a NiFe-LDH layer on a substrate through electrodeposition; and (B) forming a ceramic layer of Formula 1 on the NiFe-LDH layer by vacuum thermal evaporation deposition of ball-milled ceramic powder.

[0118] Another aspect of the present invention relates to a method for manufacturing a layered heterostructure composite comprising the steps of: (A) forming a NiFe-LDH nanostructure on a carbon cloth substrate by electrodeposition; and (B) forming a plurality of ceramic nanoparticles represented by Formula 1 on the nanostructure by vacuum thermal evaporation.

[0119] The above-described manufacturing method of the present invention is considered to have a distinctive advantage in that it enables the production of a composite composed of a ceramic layer / NiFe-LDH layer / substrate or a ceramic nanoparticle / NiFe-LDH nanostructure / substrate, or an electrode containing the same, without using a separate binder. While strong adhesion between the components is secured without the use of a separate binder, conductivity and accessibility to the active site can be significantly improved due to the absence of a separate binder.

[0120] Furthermore, according to the method of the present invention, the ceramic powder is evaporated in a vacuum state through a thermal evaporation system due to high-temperature heating, and the vapor particles move to reach the substrate directly and are converted back into a solid state. Therefore, not only is the structural integrity of the material guaranteed during this solidification process, but it also has the advantage of allowing active components to be uniformly distributed across the entire substrate.

[0121] In addition, the high vacuum environment adopted in the method of the present invention not only minimizes the incorporation of impurities into the substrate, but also adopts a thermal evaporation method that does not use any solvent, thereby eliminating the problem of damage to the lower part of the substrate caused by the use of solvents in existing technologies, which is of great significance to the method of the present invention.

[0122] According to one embodiment, the method further includes a step of pre-treating a carbon cloth substrate before step (A).

[0123] The above pretreatment step includes removing surface oxides and contaminants by sequential ultrasonic cleaning with HCl, KOH, and deionized (DI) water for 15 minutes each. After ultrasonic treatment, the carbon cloth is dried overnight in a vacuum oven at 60 °C to prevent oxidation before electrodeposition.

[0124] According to one embodiment, the electrodeposition of step (A) is performed with a three-electrode configuration.

[0125] The above 3-electrode configuration uses a saturated Hg / HgO electrode or an Ag / AgCl electrode as the reference electrode, and platinum foil (1×1 cm 2 , 99.99% purity, 0.5 mm thickness) is used as the counter electrode, and pre-treated carbon cloth is used as the working electrode.

[0126] According to another embodiment, the electrodeposition of step (A) is performed in an electrodeposition bath with a pH of 2.0-3.0, preferably 2.2±0.5.

[0127] According to another embodiment, the electrodeposition of step (A) is performed at an applied potential of -1.0±0.5 V relative to Hg / HgO, preferably -1.5±0.2 V.

[0128] According to another embodiment, the electrodeposition time of step (A) is 7-13 minutes, preferably 10±3 minutes.

[0129] According to another embodiment, the electrodeposition bath is prepared by dissolving 16 mmol of Ni(NO3)2·6H2O, 10 mmol of Fe(NO3)3·9H2O, and 1.0 mmol of CH3COOK in 250 mL of deionized water. The solution is magnetically stirred at 400 rpm for 30 minutes at room temperature (25±3 °C) to ensure complete dissolution and homogeneity.

[0130] According to another embodiment, the effect of electrodeposition time on NiFe-LDH characteristics was systematically investigated over 2, 4, 6, 8, 10, 12, 15, and 20 minutes, and the optimal deposition time was confirmed through comprehensive electrochemical characterization.

[0131] According to another embodiment, after electrodeposition, each electrode is carefully removed from the electrodeposition bath and washed sequentially with deionized water and ethanol to remove residual precursor ions and electrolytes. The electrode is then dried overnight at 60 °C under vacuum conditions and stored in a desiccator at room temperature to prevent hydration and surface oxidation.

[0132] According to one embodiment, the vacuum thermal evaporation method is performed by evaporating the ball-milled powder of the ceramic nanoparticles in a reduced pressure chamber in which the NiFe-LDH nanostructure is located.

[0133] The above thermal evaporation is carried out in a vacuum chamber equipped with a rotary vane pump (base pressure ≤1×10⁻⁴ Pa), a tungsten crucible for the evaporation source, and a substrate holder located 15 cm above the evaporation source.

[0134] According to another embodiment, ball-milled ceramic powder (0.5-1.0 g) is loaded into a crucible and heated to 700±20 °C to achieve optimal vapor pressure without decomposition.

[0135] According to another embodiment, the NiFe-LDH / CC substrate from the electrodeposition is maintained at 300±30 °C through gentle substrate heating.

[0136] According to another embodiment, evaporation is 1-5×10 -4 It is performed at a deposition rate of 0.5-1.5 nm / s at a chamber pressure of Pa and monitored in real time through a quartz crystal microbalance (QCM).

[0137] According to another embodiment, evaporation is carried out for 15-20 minutes to deposit a uniform ceramic layer of 10-15 nm thickness on the NiFe-LDH surface.

[0138] According to another embodiment, when the target film thickness is achieved in the QCM sensor, heating is immediately stopped and the chamber is naturally cooled (within 30-60 minutes until the crucible temperature <100 °C). Afterward, the chamber is vented with dry nitrogen gas, and the S4 electrode (ceramic / NiFe-LDH / CC) is removed and immediately stored in a desiccator at room temperature to prevent moisture absorption and surface oxidation.

[0139] Thermal evaporation was selected due to its superior scalability compared to sputtering or pulsed laser deposition, lower equipment costs (~$50-200k vs. $200-500k of alternatives), and high material utilization (70-90% vs. 30-50% of sputtering). QCM thickness monitoring, source temperature calibration against optical pyrometers, and batch documentation of vacuum conditions ensure reproducible deposition across multiple electrodes and enable seamless technology transfer to industrial roll-to-roll manufacturing systems.

[0140] According to one embodiment, the ceramic ball milling powder is Pb 7.38 Cu 2.62 (PO4) 5.46 (SO4) 0.54 O 0.66 S 0.84 A ceramic of the composition is manufactured by ball milling at 200-600 rpm for 2-12 hours, preferably at 450-550 rpm for 5-7 hours, and more preferably at 500 rpm for 6 hours.

[0141] The present invention is to be explained in more detail below through examples, etc.; however, the scope and content of the present invention shall not be interpreted as being narrowed or limited by the examples, etc. below. Furthermore, based on the disclosure of the present invention including the examples below, it is evident that a person skilled in the art can easily practice the present invention even without specific experimental results presented, and it is natural that such variations and modifications fall within the scope of the appended claims.

[0142] Furthermore, the experimental results presented below describe only the representative experimental results of the above examples and comparative examples, and the respective effects of various embodiments of the present invention not explicitly presented below will be described in detail in the relevant sections.

[0143] Examples

[0144] Chemicals and materials

[0145] Iron(III) nitrate hexahydrate (Fe(NO3)3·9H2O), nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O), potassium acetate (CH3COOK), hydrochloric acid (HCl), acetone, and ethanol were used without further purification. 3×1 cm 2 A carbon cloth (CC) substrate of a certain size was used as the working electrode and deposition platform.

[0146] Preparation Example 1: Ceramic Preparation

[0147] Powders of PbO, PbSO4, Cu, and P were prepared in the molar ratios of the molecules to be produced and uniformly mixed. The mixture was placed in a reaction tube (quartz or copper tube), vacuum was created, and the tube was sealed. The reaction was carried out by heating at 770 °C for 12 hours in the first stage. After the reaction was completed, the granules formed in the reaction tube were powdered, and the pressure was reduced to a near-vacuum state and heated at 550 °C for 5 hours in the second stage. Through this process, solid sulfur was sublimated, and the ceramic was produced by removing the sublimated sulfur in the molar ratio through an evacuation process.

[0148] For example, when manufacturing a ceramic with a Cu doping amount controlled to 2 moles, the raw materials are mixed with a molar ratio of PbO : PbSO4 : Cu : P = 2 : 6 : 2 : 6, and as another example, the composition is Pb 7.38 Cu 2.62 (PO4) 5.46 (SO4) 0.54 O 0.66 S 0.84 When manufacturing the ceramic, the raw materials were mixed with a molar ratio of PbO : PbSO4 : Cu : P = 1.38 : 6 : 2.62 : 6.

[0149] Manufactured Pb 7.38 Cu 2.62 (PO4) 5.46 (SO4) 0.54 O 0.66 S 0.84Ball-milled ceramic powder was obtained by ball-milling a ceramic (structure confirmed through XPS and XRD, etc., and average molecular weight confirmed to be 2,303) at 500 rpm for 6 hours.

[0150] Preparation Example 2: Substrate Pretreatment

[0151] 3×1 cm to be used as working electrode and deposition platform 2 A carbon cloth (CC) substrate of size was ultrasonically cleaned sequentially in HCl, KOH, and deionized water (DI water) for 15 minutes each to completely remove surface oxides and contaminants. After cleaning, it was dried overnight in a vacuum oven at 60°C to prevent oxidation before electrodeposition.

[0152] Comparative Manufacturing Example 1: Ceramic Manufacturing

[0153] After preparing Pb9Cu(PO4)6O (CAS No. 2972464-09-6) according to the known method, such as Chemistry of Materials (2024), 36(1), 275-285, ball milling was performed in the same manner as in Preparation Example 1 above.

[0154] Comparative Manufacturing Example 2: Ceramic Manufacturing

[0155] Pb9Cu(PO4) according to the method described in Korean Published Patent No. 10-2023-0030188 5.5 (SO4) 0.5 S 3.5 After manufacturing, ball milling was performed in the same manner as in Manufacturing Example 1 above.

[0156] Example 1: Preparation of Ceramic / NiFe-LDH / CC Electrode (S4)

[0157] (1) NiFe-LDH electrodeposition

[0158] The carbon cloth substrate was thoroughly cleaned of surface oxides and contaminants by sequential ultrasonic cleaning with HCl, KOH, and deionized (DI) water for 15 minutes each. After ultrasonic treatment, the carbon cloth was dried overnight in a vacuum oven at 60°C to prevent oxidation before electrodeposition.

[0159] An electrodeposition bath was prepared by dissolving 16 mmol Ni(NO3)2·6H2O, 10 mmol Fe(NO3)3·9H2O, and 1.0 mmol CH3COOK in 250 mL of deionized water. The solution was stirred at 400 rpm for 30 minutes at room temperature (25±3 ℃) to ensure homogeneity. Electrodeposition was performed using a saturated Hg / HgO reference electrode and a platinum foil (1×1 cm²). 2 It was performed with a three-electrode configuration consisting of a counter electrode and a pre-treated carbon cloth working electrode.

[0160] To optimize the deposition potential, CV was performed at a slow scan rate of 2 mV / s in a potential window from -1.8 V to +0.5 V (vs. Hg / HgO), confirming a reduction potential of approximately -0.8 V. Based on this, electrostatic deposition was performed at -1.5 ± 0.2 V (vs. Hg / HgO). The pH of the deposition bath was maintained at 2.5 ± 0.5 throughout the entire process. NiFe-LDH / CC was fabricated by deposition for an optimal deposition time of 10 minutes.

[0161] (2) Ceramic thermal evaporation deposition

[0162] Vacuum chamber equipped with rotary vane pump (base pressure ≤1×10 -4 Pa), a tungsten crucible for the evaporation source, and a substrate holder positioned 15 cm above the evaporation source were used. The ceramic powder (0.8 g) ball-milled in Preparation Example 1 was placed in the crucible and heated to 700±20 ℃. The NiFe-LDH / CC substrate was maintained at 300±30 ℃. The deposition was 1-5×10 -4 Ceramic / NiFe-LDH / CC was fabricated by performing the process at a speed of 0.5-1.5 nm / s under Pa pressure and collecting the sample after achieving a target thickness (10-15 nm) (named 'S4').

[0163] Comparative Examples 1 and 2: Preparation of Ceramic / NiFe-LDH / CC Electrodes

[0164] A composite electrode was prepared in the same manner as in Example 1, except that the ceramic prepared in Comparative Examples 1 and 2 was used instead of the ceramic prepared in Example 1 (Comparative Examples 1 and 2, respectively).

[0165] Comparative Examples 3-6: Preparation of various layer sequence variant electrodes

[0166] (1) Carbon cloth (CC) was prepared to be used as an electrode without electrodeposition (Comparative Example 3, named 'S1').

[0167] (2) NiFe-LDH / CC was prepared in the same way as in ‘(1) NiFe-LDH electrodeposition’ of Example 1 above (Comparative Example 4, named ‘S2’).

[0168] (3) A NiFe-LDH / ceramic / CC electrode was prepared by proceeding in the same manner as in Example 1 above, except that instead of preparing NiFe-LDH / CC by electrodepositing NiFe-LDH on a CC substrate and then thermally evaporating a ceramic onto it, a ceramic / CC was prepared by thermally evaporating a ceramic onto CC and then electrodepositing NiFe-LDH onto it (Comparative Example 5, named 'S3').

[0169] (4) After preparing the ceramic / NiFe-LDH / CC as in Example 1 above, a three-layer structured NiFe-LDH / ceramic / NiFe-LDH / CC electrode was prepared by electrodepositing NiFe-LDH again (Comparative Example 6, named 'S5').

[0170] Specific processes not described above are as described in Example 1.

[0171] Test Example 1: Raman Spectroscopic Analysis

[0172] To analyze vibration characteristics and structural features, the above S2 to S5 electrodes were analyzed using Raman spectroscopy (λexc=532nm laser, 1-5 mW output).

[0173] (1) Pure S2 electrode

[0174] For the S2 electrode, which is pure NiFe-LDH / CC, 460-480 cm -1 (Fe 3+ / Ni 2+ -O-Ni 2+ and Fe 3+ -O-Fe 3+ Metal-oxygen stretching), 515-560 cm -1 (MO expansion, M=Ni or Fe), and 640-730 cm -1 Characteristic vibrational bands were exhibited in (symmetric stretching of Ni-O and Fe-O bonds and Ni-O-Fe bridging interactions).

[0175] Also, 3440 cm -1 The broad band in the vicinity represents structural OH within the LDH framework. - It corresponded to the hydroxyl group stretching vibrations of surface-adsorbed water molecules.

[0176] In addition, interlayer nitrate ions (NO₃⁻) 3- The peak is approximately 1377 cm -1 It was observed that nitrate counterions exist in the LDH interlayer space.

[0177] (2) Composite electrodes S3 to S5

[0178] The structural integrity was confirmed in the composite electrodes S3, S4, and S5, as the NiFe-LDH characteristic band was preserved.

[0179] In addition to this, Cu-O expansion (~400-500 cm -1 ), PO expansion (~600-700 cm) -1 ), Pb-O expansion (~400-600 cm -1 New Raman bands attributed to vibration modes of the ceramic secondary phase, including ) at 200–500 cm⁻¹ -1 and 600-900 cm -1 It appeared in the area.

[0180] In addition, NiFe-LDH MO stretch band (460-480 and 515-560 cm) -1The relative intensity ratio of ) showed a slight change (3-8% variation) in the composite electrode compared to the S2 electrode, which was consistent with electronic metal-support interaction (EMSI) at the heterointerface where electron density is redistributed between NiFe-LDH and the ceramic phase. Through such Raman data, close contact and potential electronic coupling between the two phases in the composite structure can be comprehensively confirmed.

[0181] Test Example 2: High-resolution XPS analysis

[0182] High-resolution XPS was performed on the above S2 to S5 electrodes using monochromatic AlKα X-rays (hν=1486.6 eV). All binding energies were corrected to an adventitious carbon C 1s peak at 284.8 eV.

[0183] (1) Pure S2 electrode

[0184] The Ni 2p region of the S2 electrode is Ni within the LDH structure 2+ Showing a main peak at 857.6 eV and satellite splitting at a binding energy approximately 6 eV higher, which are characteristic of Ni 2+ The oxidation state was checked.

[0185] In addition, the Fe 2p region is Fe, the main iron oxidation state of NiFe-LDH. 3+ It exhibited a dominant peak at 712.0 eV assigned to it.

[0186] Additionally, the O 1s region was deconvolved into two major components: (i) metal-bonded oxygen (MO) at approximately 528.9 eV representing the lattice oxygen of the LDH framework, and (ii) hydroxyl oxygen (OH) at approximately 532.3 eV representing structural and surface hydroxyl groups.

[0187] (2) Composite electrodes S3 to S5

[0188] For the composite electrodes S3, S4, and S5, the Ni 2p and Fe 2p peak positions showed a slight shift of 0.1–0.3 eV compared to the S2 electrode, indicating electron redistribution and electronic metal-support interactions (EMSI) occurring at the heterointerface. This shift in binding energy serves as a direct basis for charge transfer between the NiFe-LDH and the ceramic phase, and the direction and magnitude of the transfer indicate the strength and nature of the electronic coupling.

[0189] In addition, new photoelectronic signals of copper and lead species appeared in the composite electrode, with Cu 2p at 932.8 eV (Cu + ) and 934.8 eV(Cu 2+ It demonstrated the major contribution of ) showing the presence of mixed valence copper species on the ceramic, and Pb on the lead-containing phase 2+ or Pb 4+ Pb 4f attributable to the species 7 / 2 It appeared at 137.8-138.6 eV, and P 2p was detected at 133-135 eV and was consistent with phosphorus in phosphide coordination.

[0190] In addition, the presence of all elements and binding energy positions confirmed that the ceramic phase was successfully integrated without decomposition into unwanted secondary phases or oxidation.

[0191] In addition, the composite electrode showed an increase in the strength of the MO component and a change in the MO to OH ratio compared to the S2 electrode as a result of O 1s deconvolution, which indicates an improvement in interfacial bonding and oxygen coordination. These changes are directly correlated with the improved electron transfer and catalytic activity observed in electrochemical measurements.

[0192] Test Example 3: SEM Analysis and EDS Elemental Mapping

[0193] SEM analysis and EDS elemental mapping were performed on the above S2 to S5 electrodes.

[0194] (1) Pure S2 electrode

[0195] SEM analysis of the S2 (pure NiFe-LDH / CC) electrode showed that carbon cloth fibers were uniformly covered with NiFe-LDH nanosheets or nanoplates (longitudinal thickness 15-30 nm, transverse size 100-300 nm), forming a hierarchical nanostructure with an enhanced surface area. Individual nanosheet features and random orientation on the fiber surface are characteristics of the electrodeposited NiFe-LDH.

[0196] (2) Composite electrodes S3 to S5

[0197] The composite electrodes S3, S4, and S5 showed distinctly modified forms reflecting their layer sequence architecture.

[0198] First, the S3 electrode (NiFe-LDH / ceramic / CC) exhibited a double-layer structure confirmed by cross-sectional SEM images showing NiFe-LDH nanosheets deposited on a base layer of thermally evaporated ceramic material.

[0199] The S4 electrode (ceramic / NiFe-LDH / CC) was based on a NiFe-LDH nanosheet layer and showed an conformal or partial conformal coating of ceramic (estimated thickness 5-20 nm) deposited on its surface by thermal evaporation.

[0200] EDS elemental mapping results confirmed a uniform distribution of all elements. Iron (Fe) and nickel (Ni) were concentrated in the LDH-containing region, while copper (Cu), lead (Pb), and phosphorus (P) were concentrated in the ceramic-containing region. Elemental line scan analysis across the layer boundaries revealed sharp compositional transitions at electrodes S3 and S4, confirming the formation of discontinuous and well-defined layers rather than interdiffused phases.

[0201] Test Example 4: TEM analysis, annular dark-field (ADF) STEM imaging, and STEM-EDS elemental mapping

[0202] TEM analysis, annular dark-field (HAADF) STEM imaging, and STEM-EDS elemental mapping were performed on the above S2 to S5 electrodes.

[0203] (1) Pure S2 electrode

[0204] TEM analysis at 200 kV showed that the S2 electrode had a well-aligned crystal lattice with interplanar spacing consistent with the (012) plane (~2.6) of the NiFe-LDH structure, and showed high crystallinity with minimized surface amorphization due to clear lattice fringes.

[0205] (2) Composite electrodes S3 to S5

[0206] TEM analysis at 200 kV revealed that the composite electrodes exhibited significant heterointerface structures. Electrode S4, the optimal composition exhibiting the best OER performance, showed a distinct heterointerface region between the NiFe-LDH layer and the ceramic coating with the following characteristics.

[0207] (i) Visible misalignment dislocations and blade dislocations observed across the heterogeneous interface over a range of about 1–5 nm (which indicates the presence of interfacial deformation),

[0208] (ii) Point defects, oxygen vacancies, and potential short-range order changes at heterointerfaces acting as highly active catalytic sites,

[0209] (iii) Clear atomic resolution contrast distinguishing NiFe-LDH and ceramic phases with sharp interfaces in most areas (this demonstrates excellent heterointerface contact),

[0210] (iv) Direct contact between two crystalline phases without a significant amorphous interface region (this ensures efficient electron transfer).

[0211] In addition, the results of annular dark-field (HAADF) STEM imaging and STEM-EDS elemental mapping confirmed the spatial distribution of Fe, Ni, Cu, Pb, and P, along with distinct phase boundaries where interdiffusion was minimized, particularly at the S4 electrode where NiFe-LDH served as the substrate contact layer.

[0212] Test Example 5: Electrochemical Measurement

[0213] (1) Test method

[0214] All electrochemical measurements were performed using a BioLogic VMP3 multichannel potentiostat in a three-electrode electrochemical cell configuration. The working electrodes consisted of fabricated catalyst electrodes (S1-S5) deposited on carbon cloth (geometric area = 1 cm²). 2 ). Platinum foil electrode (1×1 cm 2 A saturated Hg / HgO electrode (99.99% purity, 0.5 mm thickness) was used as the counter electrode, and a saturated Hg / HgO electrode (1 M KOH, +0.197 V relative to the standard hydrogen electrode) was used as the reference electrode. The three electrodes were immersed in a 1 M KOH aqueous alkaline electrolyte prepared by dissolving potassium hydroxide (KOH, >98% purity) in deionized water. The electrolyte was stirred at 400 rpm during all measurements to ensure homogeneous solution conditions. All electrochemical measurements were performed at a controlled room temperature (25 ± 2 °C) to minimize temperature-related variations in the electrochemical response.

[0215] (2) Potential conversion to the RHE scale

[0216] All measured potentials reported in this specification were converted from the Hg / HgO reference scale to the reversible hydrogen electrode (RHE) scale using the following standard conversion equation:

[0217] E(RHE) = E(Hg / HgO + 0.242 V + 0.059 × pH

[0218] For 1 M KOH (approx. pH = 14) at 25 °C, the conversion offset is approximately +0.887 V. This conversion ensures that all reported overpotential values ​​can be directly compared with literature data measured against the RHE standard.

[0219] (3) Linear sweep voltammetry (LSV) for OER activity evaluation

[0220] Linear sweep voltammetry was performed to evaluate the oxygen evolution reaction activity of all catalytic electrodes (S1–S5). Prior to LSV measurements, each catalytic electrode was electrochemically conditioned by performing three cyclic voltammetry (CV) scans at a scan rate of 50 mV / s between 0.8–1.8 V relative to the RHE to stabilize the catalyst surface and remove surface contaminants or loosely bound species. After conditioning, LSV measurements were recorded in the anode (oxidation) direction at a slow scan rate of 10 mV / s in the potential range of 1.4–2.2 V relative to the RHE. The current response was recorded sequentially as a function of applied potential to generate a linear sweep voltammetry curve representing the characteristic S-shaped polarization curve of water oxidation. Overpotentials were measured at potentials where each current density was achieved at 10, 50, 100, and 300 mA / cm². 2 It was extracted from the LSV curve at the standardized current density.

[0221] (4) Tafel slope analysis

[0222] The Tafel slope (also known as the Tafel equation or Tafel parameter) was extracted from LSV data by constructing a Tafel plot representing the relationship between the overvoltage (η) and the logarithm of the current density (log j) according to the Tafel equation:

[0223] η = a + b·log(j)

[0224] Here, η is the overvoltage (mV) and j is the current density (mA / cm²). 2), a is the intercept (related to exchange current density), and b is the Tafel slope (mV / decade). The Tafel slope was determined through linear regression of the LSV data in the low overpotential region (typically 50–150 mV above the onset potential) where reaction kinetics are rate-limited by charge transfer rather than mass transfer. A lower Tafel slope indicates faster electrochemical kinetics and more favorable oxygen intermediate stabilization at the catalyst surface. For comparative analysis, the Tafel slopes of all electrodes (S1–S5) were extracted from the same potential region to ensure direct comparability.

[0225] (5) Electrochemical Impedance Spectroscopy (EIS)

[0226] Electrochemical impedance spectroscopy was performed to evaluate interfacial charge transport kinetics and resistance at the catalyst / electrolyte interface. EIS measurements were taken at 300 mA / cm² for each electrode to ensure standardized measurement conditions across all electrodes. 2 The procedure was performed at a fixed potential corresponding to the overvoltage (determined from LSV measurements). A sinusoidal AC voltage perturbation with an amplitude of 10 mV was applied over a wide frequency range of 100 kHz to 0.1 Hz, and measurements were taken at 20 points per decimal (logarithmic intervals) to fully capture the impedance response across all relevant time scales. The measured electrochemical impedance data were displayed in the form of a Nyquist plot (imaginary impedance vs. real impedance components), where the characteristic semicircular arc diameter represents the charge transfer resistance (R) at the catalyst / electrolyte interface. ct It directly reflects ). Charge transfer resistance directly reflects the solution resistance (Rs) and charge transfer resistance (R) from the Nyquist data. ct It was extracted by fitting to an equivalent electrical circuit model consisting of a parallel combination of constant phase elements (CPEs) representing the electrochemical double layer: Rs + [R ct∥ CPE]. This circuit model is the standard for a single-step Faraday reaction in a porous electrode.

[0227] (6) Determination of electrochemical active surface area (ECSA)

[0228] The electrochemical active surface area (ECSA) was determined from cyclic voltammetry (CV) measurements in the non-Faraday potential region, where only charging and discharging of the electric double layer occur without electrochemical reactions. CV scans were performed at progressively increasing scan rates of 20, 40, 60, 80, and 100 mV / s between 1.1 and 1.3 V relative to the RHE (region without Faraday oxygen evolution current). The double layer capacitance (Cdl) was extracted by plotting the cathode current (at 1.2 V relative to the RHE, the center of the potential window) as a function of scan rate. A linear relationship between current and scan rate was observed, and the slope of the linear regression was equal to twice the double layer capacitance (Cdl = slope / 2). The ECSA was subsequently calculated using the following equation:

[0229] ECSA (cm 2 ) = Cdl / Cf

[0230] Here, Cdl is the measured double-layer capacitance (mF / cm²). 2 ) and Cf is the specific capacitance of the material surface (typically 0.0201 mF / cm² for carbon and transition metal oxide / hydroxide surfaces in alkaline media). 2 (assumed to be). This ECSA value represents the electrochemically active surface area per geometric area of ​​the electrode and provides an estimate of the density and accessibility of catalytic active sites.

[0231] (7) Test results

[0232] The electrochemical activity of the various electrodes prepared above was evaluated, and the results are presented in Table 1 and Figure 2.

[0233] Above S1 to S5 electrodes (1 cm 2Each geometric area was used as the working electrode, the platinum foil as the counter electrode, and the saturated Hg / HgO electrode as the reference electrode, and measurements were taken in a 1 M KOH aqueous solution (approx. pH = 14), showing the following OER performance evaluation results.

[0234] electrode Overvoltage @300 mA / cm 2 (mV) Tafel slope (mV / dec) R ct (Ω·cm 2 ) ECSA(cm 2 ) S1 (Bear CC) 959 167.2 5.47 - S2 (NiFe-LDH / CC) 660 139.6 2.85 180.2 S3 (NiFe-LDH / Ceramic / CC) 586 109.7 2.12 225.6 S4 (Ceramic / NiFe-LDH / CC) 493 79.3 1.35 304.5 S5 (3-story structure) 522 84.8 1.78 268.3

[0235] In particular, 300 mA / cm² for the S4 electrode 2 As a result of performing a 20-hour continuous operation test at a high current density, it was confirmed that more than 90% of the activity was continuously maintained.

[0236] Furthermore, as can be seen from the linear sweep voltammetry (LSV) polarization curve in Fig. 2(a) and the comparison of overvoltages at various current densities in Fig. 2(f), the S4 heterostructure (ceramic / NiFe-LDH / CC) exhibits 300 mA / cm² 2 It showed an oxygen evolution overpotential of 493 mV, demonstrating a performance improvement of 167 mV (25.3%) compared to pure NiFe-LDH (S2: 660 mV) and 466 mV (48.6%) compared to bare carbon cloth (S1: 959 mV).

[0237] As can be seen from the Tafel slope values ​​in Fig. 2(b), S4 exhibited the lowest Tafel slope of 79.3 mV / dec, showing the fastest electrochemical kinetics. In contrast, S2 (139.6 mV / dec), S3 (109.7 mV / dec), and S5 (84.8 mV / dec) all showed higher Tafel slopes, confirming that the layer sequence of S4 is optimal for enhancing OER kinetics.

[0238] As can be seen from the EIS Nyquist plot in Fig. 2(c), S4 is 1.35 Ω·cm 2 The lowest charge transfer resistance (R ctIt showed a value reduced by 75.3% compared to bare CC. This confirms the excellent electron transfer efficiency between NiFe-LDH and ceramic in the S4 structure.

[0239] As can be seen from the double-layer capacitance (Cdl) measurements and ECSA values ​​in Figures 2(d) and 2(e), S4 exhibited the highest electrochemical active surface area (ECSA) of 304.5 cm2, confirming abundant and accessible catalytic active sites.

[0240] In particular, evaluation results through systematic variations (S2, S3, S4, S5) showed that the ceramic / NiFe-LDH sequence (S4: 493 mV) exhibited 93 mV better performance than the reverse sequence, the NiFe-LDH / ceramic sequence (S3: 586 mV), establishing that layer position is an important and non-trivial design parameter. The S4 configuration achieves an optimal balance between electron transfer (substrate contact NiFe-LDH) and oxygen evolution catalysis (surface ceramic), whereas the reverse sequence of S3 causes an interfacial conductivity bottleneck.

[0241] As described above, in an embodiment of the present invention, a layered heterostructure composite that can be used as an electrode catalyst for OER in the field of water electrolysis was prepared by vacuum deposition of a ceramic material of Formula 1 using a thermal evaporation system on a nickel-iron layered double hydroxide (NiFe-LDH) grown by electrodeposition on a carbon cloth (CC) substrate.

[0242] In addition, the composites prepared in Comparative Example 1 and Comparative Example 2, respectively, and the composite of Example 1 were compared and evaluated under the same conditions, and the following significant differences were confirmed.

[0243] In the case of the composite of Example 1, (i) electron redistribution occurs due to electronic metal-support interaction (EMSI) between NiFe-LDH and the ceramic, resulting in a binding energy shift of 0.1–0.3 eV of the Ni 2p and Fe 2p peaks observed in XPS analysis; (ii) consequently, a low overpotential of 493 mV and a Tafel slope of 79.3 mV / dec are achieved at 300 mA / cm²; and (iii) the enhanced electrical conductivity of the ceramic layer forms an efficient electron transfer path at the interface with the NiFe-LDH layer, thereby lowering the charge transfer resistance (R ct ) is 1.35 Ω·cm 2 It showed positive heterogeneous effects in that it was significantly reduced and (iv) more than 90% of the activity was stably maintained even after 20 hours of continuous operation.

[0244] On the other hand, in Comparative Examples 1 and 2, (i) no significant binding energy shift of the Ni 2p and Fe 2p peaks was observed in XPS analysis, indicating the absence of electronic interaction between NiFe-LDH and the ceramic, and (ii) 300 mA / cm² 2 (iii) the overvoltage is found to be 720 mV or higher and 680 mV or higher, respectively, which is 200 mV or higher than that of the example, and (iii) the electrical conductivity of the ceramic itself is significantly lower than that of the ceramic in the example, causing a conductive bottleneck at the interface and a charge transfer resistance of 3.5 Ω·cm 2 (iv) Since a durability problem is observed in which the activity rapidly decreases to less than 70% during continuous operation within 10 hours, a composite of various embodiments of the present invention including the composite of Example 1 is preferred.

[0245] These results demonstrate that the compositional range of Cu doping amount (x = 0.9-9.9), sulfate group substitution amount (y), and oxygen / sulfur content (z, z') specified in Chemical Formula 1 is essential for improving electrical conductivity through changes in the band structure of the ceramic and for exhibiting electronic synergy with NiFe-LDH, and confirm that the technical effects of the present invention cannot be achieved when the compositional range is exceeded as in Comparative Examples 1 and 2.

Claims

Claim 1 A layered heterostructure composite for a water electrolysis electrode catalyst comprising (a) a substrate, (b) a substrate contact layer located on the substrate and comprising a nickel-iron layered double hydroxide (NiFe-LDH), and (c) a surface active layer which is a coating layer located on the substrate contact layer and comprising ceramic nanoparticles; wherein the ceramic is a layered heterostructure composite for a water electrolysis electrode catalyst represented by the following chemical formula: [Chemical Formula 1]Pb 10-x Cu x [(PO4) 6-y (SO4) y ]O z S z' x is a real number between 0.9 and 9.9, and y is 10 -10 It is a real number from 5.9 to 10, where z and z' are each 10 -10 It is a real number between 4 and 10, and z+z' is 10 -10 It is a mistake of up to 4. Claim 2 In claim 1, the substrate contact layer is formed by electrodepositing a nickel-iron layered double hydroxide (NiFe-LDH) on the substrate, and the surface active layer is formed by thermal evaporation deposition of the ceramic on the substrate contact layer, forming a layered heterostructure composite. Claim 3 In claim 1, the above-described contact layer is a layered heterostructure composite having a plurality of nanosheets or nanoplatelets having a longitudinal thickness of 15-30 nm and a transverse size of 100-300 nm. Claim 4 A layered heterostructure composite according to claim 3, wherein each of the plurality of nanosheets is structurally connected to an adjacent nanosheet to form a hierarchical nanostructure, and at least 60% of the plurality of nanosheets are formed in a random orientation on the surface of the substrate. Claim 5 A layered heterostructure composite according to claim 1, wherein the surface active layer has a thickness of 5-20 nm and is positioned on the surface of the substrate contact layer as a conformal or partially conformal coating. Claim 6 In claim 1, the ceramic is a unit area (cm²) of the above-described material. 2 Layered heterostructure complex containing 1-10 mg per ) Claim 7 In claim 1, the layered heterostructure composite is 2.1-9.

9. Claim 8 In claim 1, the complex, based on the results of Raman spectroscopic analysis, Cu-O stretching (~400-500 cm -1 ), PO expansion (~600-700 cm) -1 ), Pb-O expansion (~400-600 cm -1 Raman bands attributable to vibration modes of the ceramic secondary phase, including ) at 200-500 cm -1 and 600-900 cm -1 Visible in the region, NiFe-LDH MO stretch band (460-480 and 515-560 cm) -1 A layered heterostructure composite showing a relative strength ratio of ) with a variation of 3-8% compared to pure NiFe-LDH. Claim 9 The layered heterostructure composite of claim 1, wherein, as a result of X-ray photoelectron spectroscopy (XPS) analysis, the Ni 2p and Fe 2p peak positions are shifted by 0.1-0.3 eV relative to pure NiFe-LDH to exhibit electronic metal-support interaction (EMSI), and as a result of O 1s deconvolution, the intensity of the MO component increases relative to pure NiFe-LDH and the MO to OH ratio changes. Claim 10 In claim 1, the composite forms a heterostructured composite having a heterostructured interface comprising misfit potentials and / or blade potentials in the range of 1-5 nm between the substrate contact layer and the surface active layer based on HRTEM analysis results, and including point defects and oxygen vacancies in the heterostructured interface region. Claim 11 An electrode catalyst for water electrolysis comprising a layered heterostructure composite for a water electrolysis electrode catalyst according to any one of claims 1 to 10. Claim 12 In claim 11, the above-mentioned electrode catalyst for water electrolysis is an electrode catalyst for an oxygen evolution reaction (OER). Claim 13 An electrode for water electrolysis comprising a layered heterostructure composite for a water electrolysis electrode catalyst according to any one of claims 1 to 10. Claim 14 In paragraph 13, the above-mentioned electrode for water electrolysis is an electrode for water electrolysis for oxygen generation reaction. Claim 15 A water electrolysis device comprising a layered heterostructure composite for a water electrolysis electrode catalyst according to any one of claims 1 to 10. Claim 16 In claim 15, the layered heterostructure composite is included in an anode for an oxygen evolution reaction, said anode is a binder-free electrode that does not contain a binder, and said water electrolysis device is a reaction chamber for an alkaline electrolyte and 200 mA / cm² 2 The water electrolysis device includes a power supply for abnormal operation, and the water electrolysis device adopts an alkaline electrolyte. Claim 17 A method for manufacturing a layered heterostructure composite comprising: (A) a step of forming a NiFe-LDH layer on a substrate through electro-deposition; (B) a step of forming a ceramic layer on the NiFe-LDH layer by vacuum thermal evaporation deposition of ball-milled ceramic powder; wherein the ceramic is a layered heterostructure composite for a water electrolysis electrode catalyst represented by the following Chemical Formula 1: [Chemical Formula 1]Pb 10-x Cu x [(PO4) 6-y (SO4) y ]O z S z' x is a real number between 0.9 and 9.9, and y is 10 -10 It is a real number from 5.9 to 10, where z and z' are each 10 -10 It is a real number between 4 and 10, and z+z' is 10 -10 It is a mistake of up to 4. Claim 18 In claim 17, the above step (A) is performed for 8-12 minutes using Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, CH3COOK under conditions of -1.5±0.2 V vs. Hg / HgO pH 2.5±0.5, and the vacuum thermal evaporation deposition is performed at a base pressure of 1×10⁻⁶ -4 A method for manufacturing a layered heterostructure composite, wherein the ball-milled ceramic powder is heated to 680-720 ℃ and evaporated in a reduced pressure chamber of Pa or less, and the substrate on which the NiFe-LDH layer is formed is maintained at 270-330 ℃ at a speed of 0.5-1.5 nm / s.

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