Interlayer coupling reduced graphene oxide film, and preparation method and application thereof

Abstract

The application discloses an interlayer-coupled reduced graphene oxide (rGO) film, a preparation method and application thereof. Although single-layer graphene sheets have excellent intrinsic thermal conductivity, stacked graphene films have serious thermal anisotropy and poor out-of-plane thermal transport performance due to weak van der Waals interaction between layers. The application discloses a strategy for scalable preparation of an interlayer-coupled rGO film, which is connected by covalent carbon bonds between stacked layers. A representative 200 μm-thick film prepared by the strategy has in-plane and out-of-plane thermal conductivities of 1465±63 W·m ‑1 ·K ‑1 and 14.0±1.2 W·m ‑1 ·K ‑1 , respectively. Under an extreme heat flux of 1200 W·cm ‑2 , the film can reduce temperature by 110℃ within 20 s and has excellent cycle stability. The film has high thermal and electrical conductivity, and can realize fast, uniform and durable electrothermal heating, and can be applied to the field of advanced thermal management.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology and relates to a graphene product, specifically an interlayer coupled ultrathick reduced graphene oxide film, and more particularly provides an ultrathick graphene film, a representative film with a thickness of 200 μm, which has excellent out-of-plane thermal conductivity and in-plane thermal conductivity. Background Technology

[0002] With the continuous miniaturization of electronic and optoelectronic devices, efficient thermal management has become crucial in various fields such as high-power electronics, artificial intelligence processors, light-emitting diodes, photovoltaic cells, and energy storage systems. High thermal conductivity materials play a key role in heat dissipation by rapidly transferring localized heat from hot spots in all directions. Traditionally used metallic materials (such as copper and aluminum) have thermal conductivity of approximately 400 W·m. -1 ·K -1 and 237 W·m -1 ·K -1 In advanced applications where heat flux densities can reach hundreds or even thousands of watts per square centimeter, the thermal performance of metallic materials often falls short of requirements. Furthermore, metallic materials are typically dense, rigid, and easily oxidized. In contrast, carbon-based materials, with their low density and strong covalent bonds, represent a highly promising alternative. Highly oriented pyrolytic graphite (HOPG) exhibits strong in-plane sp[…]. 2 Covalent bonds result in high in-plane phonon transport efficiency and in-plane thermal conductivity of 1500-2000 W·m. -1 ·K -1 However, HOPG has extremely low out-of-plane thermal conductivity (<8 W·m) due to weak interlayer van der Waals coupling. -1 ·K -1 Furthermore, the complex and costly preparation process of HOPG limits its widespread practical application.

[0003] Graphene is currently the material with the highest known in-plane thermal conductivity, reaching 5000 W·m under ideal conditions. -1 ·K -1 However, similar to graphite, stacked graphene exhibits weak van der Waals interactions between its layers, leading to severe phonon scattering and a decrease in both in-plane and out-of-plane thermal transport properties. With increasing stacking number, phonon-phonon scattering at the interlayer interfaces causes the thermal conductivity to drop from 5000 W·m⁻¹ in monolayer graphene. -1 ·K -1 Reduced to 2500-3000 W·m for bilayer graphene -1 ·K -1 From 1500-2000 W·m to multilayer thin films -1 ·K -1 The out-of-plane thermal conductivity remains extremely low, typically between 0.1 and 5 W·m. -1 ·K-1 Researchers have explored various strategies to enhance the out-of-plane heat transfer properties of graphene assemblies, but this performance degradation is particularly severe in ultra-thick graphene assemblies with a thickness exceeding hundreds of micrometers, posing a fundamental challenge to the practical application of such materials as heat diffusion elements. Summary of the Invention

[0004] Existing techniques for addressing the strong anisotropy of thermal conductivity in macroscopic graphene-based films and the resulting limitations on out-of-plane performance disrupt in-plane phonon transport paths, impairing lateral heat transfer properties. This invention employs a novel method to prepare interlayer-coupled ultrathick reduced graphene oxide films. In addition to excellent thermal properties, graphene can be scalably prepared via chemical exfoliation and is easily processed into flexible films, coatings, and composite materials, making it a highly promising candidate material for thermal management and energy-related applications.

[0005] The present invention adopts the following technical solution.

[0006] A method for preparing an interlayer coupled reduced graphene oxide film includes the following steps: impregnating a portion of the reduced graphene oxide film with a cyanobenzene compound solution, followed by crosslinking, carbonization, and graphitization to obtain an interlayer coupled reduced graphene oxide film.

[0007] In this invention, a crosslinking reaction is carried out by Joule heating, followed by carbonization and graphitization to obtain an interlayer coupled reduced graphene oxide film.

[0008] In this invention, a chemical reduction method is used to reduce graphene films to obtain partially redox graphene films with a thickness exceeding 5 micrometers, preferably exceeding 10 micrometers, further exceeding 20 micrometers, further exceeding 30 micrometers, further exceeding 40 micrometers, further exceeding 50 micrometers, further exceeding 60 micrometers, further exceeding 70 micrometers, further exceeding 80 micrometers, further exceeding 90 micrometers, further exceeding 100 micrometers, further exceeding 110 micrometers, further exceeding 120 micrometers, further exceeding 130 micrometers, further exceeding 140 micrometers, further exceeding 150 micrometers, further exceeding 160 micrometers, further exceeding 170 micrometers, further exceeding 180 micrometers, further exceeding 190 micrometers, further exceeding 200 micrometers, or any thickness above these data.

[0009] In this invention, graphene films are obtained by forming graphene oxide (GO) sheets, which is a conventional technique.

[0010] In this invention, the cyanobenzene compound solution includes a cyanobenzene compound, an acid, and an organic solvent, wherein the acid includes hydrochloric acid.

[0011] In this invention, the cyanobenzene compound includes 1,2,4,5-tetracyanobenzene.

[0012] In this invention, the concentration of the cyanobenzene compound solution is 1 mM to 5 mM.

[0013] This invention discloses an interlayer coupled reduced graphene oxide film prepared according to the above method.

[0014] This invention discloses the application of the above-mentioned interlayer coupled reduced graphene oxide film in the preparation of conductive and / or thermally conductive materials.

[0015] This invention discloses the application of the above-mentioned interlayer coupled reduced graphene oxide film in the preparation of thermally conductive devices.

[0016] This invention discloses the application of the above-mentioned interlayer coupled reduced graphene oxide film in the fabrication of flexible thermal conductive devices.

[0017] This invention discloses the application of the above-mentioned interlayer coupled reduced graphene oxide film in the preparation of heating devices.

[0018] This invention discloses the application of the above-mentioned interlayer coupled reduced graphene oxide film in de-icing.

[0019] The present invention discloses a heat-conducting device comprising the above-mentioned interlayer coupled reduced graphene oxide film.

[0020] The present invention discloses a heat dissipation device or a heating device, comprising the above-mentioned interlayer coupled reduced graphene oxide film.

[0021] The present invention discloses a de-icing device, comprising the above-mentioned interlayer coupled reduced graphene oxide film.

[0022] This invention develops a method for scalable fabrication of interlayer coupled rGO thin films, producing ultrathick films with both high out-of-plane and in-plane thermal conductivity. A representative 200 μm thick film exhibits an out-of-plane thermal conductivity of 14.0 ± 1.2 W·m. -1 ·K -1 At the same time, maintain 1465±63 W·m -1 ·K -1 Excellent in-plane thermal conductivity. Through a reduction process, the film retains a controllable density of residual hydroxyl groups, thereby forming interlayer aromatic ether bonds. These aromatic ether bonds are further graphitized in the stacking direction to form stable carbon bonds. This interlayer coupling effectively overcomes the inherent thermal anisotropy of stacked graphene structures, achieving efficient multidirectional heat transfer. The film maintains high thermal conductivity over a wide thickness range (thickness can be extended to 300 μm) and exhibits thermal stability at high temperatures up to 250 °C, with both in-plane and out-of-plane thermal conductivity remaining essentially unchanged. At temperatures up to 1200 W·cm⁻¹... -2Under extreme heat flux densities, a representative 200 μm thick film can reduce the temperature by 110°C within 20 seconds, exhibiting excellent cycling stability, demonstrating its reliable heat dissipation under real-world operating conditions. The ultra-thick film maintains high thermal conductivity, highlighting the effectiveness of interlayer coupling design in reducing interfacial thermal resistance as thickness increases. In addition to heat dissipation, the film's excellent electrothermal properties, scalability in thickness, and thermal stability offer new opportunities for the development of heat diffusers, thermal interface materials, and multifunctional components in next-generation high heat flux density, miniaturized electronic systems. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of out-of-plane and in-plane thermal conductivity tests.

[0024] Figure 2 The current / voltage-time curves during Joule heating show four voltage drop stages, corresponding to dehydration, covalent bonding, deoxidation and denitrification, and gradual graphitization.

[0025] Figure 3 This document illustrates the preparation method and characterization of the interlayer coupled reduced graphene oxide film of the present invention, including: (a) a schematic diagram of the film preparation process and structural evolution: starting from a partially reduced reduced graphene oxide (rGO) film, covalent aromatic ether bonds are formed through a nucleophilic aromatic substitution reaction, followed by carbonization and graphitization treatment to obtain a high-quality reduced graphene oxide structure with interlayer coupling effect; (b) a photograph of a large-area, 200 μm thick reduced graphene oxide (rGO) film; and (c) an optical photograph of the prototype device, and an infrared thermal image of the chip surface temperature distribution when using different thermally conductive materials.

[0026] Figure 4 Morphology and structure characterization of ultrathick reduced graphene oxide (rGO) films with interlayer coupling were performed and compared with initial partially reduced rGO films and control films without interlayer coupling. (a) High-resolution X-ray photoelectron spectroscopy (XPS) C1s spectra of the three samples; (b) X-ray diffraction (XRD) patterns; (c) Raman spectra; (d) Scanning electron microscopy (SEM) cross-sectional images of the interlayer coupled ultrathick films; (e) Raman mapping of the films in a 4×4 mm² region; (f) Sheet resistivity measured in regions of different sizes.

[0027] Figure 5 High-resolution XPS N 1s spectra of crosslinked rGO films in the presence / absence of HCl and under aliphatic nitrile conditions. No increase in out-of-plane thermal conductivity was observed at all oxidation levels when using aliphatic nitrile or in DMF solution without HCl.

[0028] Figure 6XPS full spectrum (a) and high-resolution C1s spectrum (b) of 10 μm thick GO film and partially reduced GO film after chemical reduction for 1 h, 3 h, 7 h and 12 h.

[0029] Figure 7 These are low-magnification and high-magnification cross-sectional SEM images of a representative ultra-thick rGO film.

[0030] Figure 8 To demonstrate that the degree of graphitization is consistent with the structural homogeneity, Raman spectra were collected from 10 randomly selected points on the interlayer coupled ultrathick rGO film.

[0031] Figure 9 The stress-strain curves of the interlayer coupled ultrathick rGO thin film are shown to demonstrate its mechanical properties.

[0032] Figure 10 To demonstrate the flexibility and adhesion of ultra-thick interlayer coupled rGO films; (a) SEM images of the cross-section of the ultra-thick interlayer coupled rGO film after repeated bending (5 cycles), compared with a control rGO film after 5 bending cycles and a commercially available graphitized polyimide film after 2 bending cycles; the ultra-thick interlayer coupled rGO film can be adhered to (b) the planar surface of a portable hard drive and (c) the surface of a CPU with sharp edges in operation. The interlayer coupled rGO film maintains structural integrity after bending.

[0033] Figure 11 To reduce the in-plane and out-of-plane thermal conductivity of graphene oxide (rGO) films; (a) in-plane and through-plane (out-of-plane) thermal conductivity of a 200 μm thick sample; (b) temperature dependence of thermal conductivity at temperatures up to 250 °C; (c) thermal conductivity comparison of a 100 μm thick rGO film with interlayer coupling to a control rGO film without interlayer coupling prepared from rGO with different reduction degrees; (d) thermal conductivity of films in the range of 100–300 μm; (e) comparison of thermal conductivity of the samples in this study with reported literature data and nominal values ​​of commercial materials; (f) thickness dependence of in-plane thermal conductivity compared with reported data; error bars represent the standard deviation calculated from multiple independent measurements.

[0034] Figure 12 Demonstration of the application of reduced graphene oxide (rGO) films with interlayer coupling in thermal management; (a) spatial temperature distribution at 4 seconds; (b) thermal performance of the sample in an actual thermal evaluation chip device (device structure shown in Figure 3c); (c) continuous operation; (d) thermal management performance during cyclic testing.

[0035] Figure 13 For the application of rGO thin films with interlayer coupling in the field of electric heating; (a) Temperature curves of rGO heating elements at different power densities; Inset: Schematic diagram of experimental setup; (b) Temperature response under step voltage change; Inset: Infrared thermal image of the thin film at a power density of 7000 W m⁻²; (c) Long-term electric heating cycle stability under alternating flat and curved states; (d) Schematic diagram and cross-sectional view of the de-icing system with insulating encapsulation; (e) Comparison of temperature changes between the ice surface and the environment during de-icing and anti-icing processes of interlayer coupled rGO thin films, non-interlayer coupled control rGO thin films, and commercial nickel-chromium (NiCr) heating elements at a power density of 7000 W m⁻²; (f) Comparison of estimated energy consumption of different heating materials.

[0036] Figure 14 The electrothermal cycling performance of an ultra-thick rGO film with interlayer coupling under 100 switching cycles (20 s on, 10 s off) demonstrates the stable operating state and reliability of the device. Detailed Implementation

[0037] Efficient thermal management remains a core challenge for high-power electronic devices due to the scarcity of materials capable of withstanding ultra-high heat flux densities (>1000 W•cm⁻²). While monolayer graphene sheets possess excellent intrinsic thermal conductivity, stacked graphene films exhibit severe thermal anisotropy and extremely poor in-plane heat transfer performance due to weak interlayer van der Waals interactions. This paper proposes a scalable strategy to construct interlayer coupled reduced graphene oxide (rGO) films linked by covalent carbon bonds. First, a partially graphene oxide film with controllable hydroxyl density is connected via a nucleophilic aromatic substitution reaction using aryl ether bridges, which are converted into stable carbon bonds during graphitization. A representative film with a thickness of 200 μm shows in-plane and out-of-plane thermal conductivity of 1465 ± 63 W·m⁻¹. -1 ·K -1 and 14.0±1.2 W·m -1 ·K -1 Furthermore, it maintains similar performance even at a thickness of 300 μm and a high temperature of 250 °C. At an extreme heat flux density of 1200 W·cm⁻², the film can reduce the temperature by 110 °C within 20 s and exhibits excellent cycling stability. Its high thermal conductivity and high electrical conductivity also endow the film with rapid, uniform, and durable electrothermal heating performance. This research provides a practical approach to overcome the inherent thermal anisotropy of graphene assemblies and can be applied to advanced thermal management fields.

[0038] In this invention, "ultra-thick" refers to a reduced graphene oxide film with a thickness exceeding 10 micrometers, further exceeding 20 micrometers, further exceeding 30 micrometers, further exceeding 40 micrometers, further exceeding 50 micrometers, further exceeding 60 micrometers, further exceeding 70 micrometers, further exceeding 80 micrometers, further exceeding 90 micrometers, further exceeding 100 micrometers, further exceeding 110 micrometers, further exceeding 120 micrometers, further exceeding 130 micrometers, further exceeding 140 micrometers, further exceeding 150 micrometers, further exceeding 160 micrometers, further exceeding 170 micrometers, further exceeding 180 micrometers, further exceeding 190 micrometers, further exceeding 200 micrometers, or any thickness above these values, such as 50 to 300 micrometers.

[0039] The present invention prepares high-quality reduced graphene oxide (rGO) films with interlayer coupling, mainly comprising three steps: (1) preparing partially reduced ultrathick rGO films; (2) immersion in 1,2,4,5-tetracyanobenzene; and (3) covalent crosslinking, carbonization, and graphitization initiated by Joule heating. Specifically, firstly, a 10 μm thick GO film is prepared by coating a graphene oxide (GO) dispersion, and then multiple 10 μm thick GO monolayers are sequentially assembled by layer-by-layer stacking to prepare a thicker film. Before each layer is stacked, the coated film is completely dried. After reaching the target thickness, hydroiodic acid (HI) is used to partially reduce the multilayer film. During this process, the residual epoxy groups (-O-) on the GO are converted into hydroxyl groups (-OH). Subsequently, the film was immersed in a dimethylformamide solution containing 1,2,4,5-tetracyanobenzene and hydrochloric acid (HCl), which allowed nitrile molecules to diffuse into the interlayer channels between adjacent layers, and the oxygen-containing functional groups on rGO interacted with the tetracyanobenzene molecules.

[0040] This invention employs Joule heating to trigger the reaction between 1,2,4,5-tetracyanobenzene and residual hydroxyl groups on graphene, forming aryl ether bonds between stacked layers. The acidic environment (HCl) enhances the electrophilicity of the aromatic rings by protonating the nitrile groups, thereby promoting the reaction. Under high current, the organic matter undergoes further carbonization through deoxygenation and denitrogenation, accompanied by graphitization and the construction of an in-plane graphene network. The recovery of the graphene network also leads to increased conductivity. Since Joule heating is an in-situ process, uniform heating across the entire film thickness can be achieved without diffusion limitations, enabling the preparation of films up to 300 μm thick. Ultimately, a high-quality, ultra-thick reduced graphene oxide film with stable interlayer coupling was obtained, exhibiting excellent thermal transfer properties both in-plane and out-of-plane. A control sample without the introduction of 1,2,4,5-tetracyanobenzene was prepared under the same conditions for comparative analysis.

[0041] The following specific experiments illustrate the technological advancements of this invention. The raw materials used are existing products, and the specific preparation operations and performance testing follow conventional techniques. Film thickness is controlled by adjusting the doctor blade height, and calibrated with a micrometer after drying. Joule heating is a standard procedure; electrodes are fabricated on both sides of the film using folded copper foil, fixed with conductive silver paste, and connected to a source for Joule heating. When increasing the current no longer results in a voltage drop, but rather a proportional increase in voltage and current, it indicates that the resistance no longer decreases, the graphitized structure is fully restored and stabilized, and the Joule heating process terminates. Graphene oxide (GO) sheets with a lateral dimension of 10-70 μm are selected for film preparation, synthesized using a modified Hummers' method, which is existing technology. The thermal diffusivity and thermal conductivity of the interlayer coupled reduced graphene oxide film in this invention are calculated using thickness measured by SEM. Unless otherwise stated, all structural and spectroscopic characterizations are performed on a 200 μm thick film, which is representative of the ultra-thick interlayer coupled graphene structure prepared in this invention. The surface conductivity of rGO thin films was measured using the van der Burg method with a Keithley 2400 multifunction source meter; see [link to relevant documentation]. Figure 1 (a) Schematic diagram of laser flare method, showing the test configuration of out-of-plane and in-plane thermal diffusivity. In the out-of-plane test, the laser pulse irradiates the lower surface of the sample and monitors the temperature rise of the upper surface. In the in-plane test of ultra-thick thin film, the cut film strips are stacked in parallel and rotated 90° so that the heat flow path is along the plane of the film. Among them, out-of-plane heat conduction: the sample is placed horizontally, the laser pulse irradiates the center of the lower surface, the infrared detector monitors the temperature rise of the center of the upper surface, and heat is transferred in one dimension along the thickness direction. The sample diameter is 12.7 mm and the lateral dimension is greater than the thickness. In-plane thermal diffusivity: the sample is cut into 5.0×10.0 mm rectangular strips, stacked vertically and rotated 90° so that the heat transfer direction is along the plane of the film.

[0042] The preparation method of an interlayer coupled reduced graphene oxide film is as follows: (1) By coating a graphene oxide (GO) dispersion (10 mg·mL) -1 A 10 μm thick GO film was prepared by GO aqueous dispersion. Then, multiple 10 μm thick GO monolayers were assembled sequentially by stacking them layer by layer to prepare a thicker film. Before each layer was stacked, the coated film was completely dried and then sprayed with a layer of water mist (without forming drips). (2) After reaching the target thickness, it is immersed in 14 wt% dilute HI aqueous solution and chemically reduced at 30°C for 7 hours. It is then washed with ethanol and deionized water and dried to obtain a partially redox graphene film. (3) Part of the redox graphene film was immersed in a DMF / HCl mixed aqueous solution containing 3 mM 1,2,4,5-benzenetetracarboxynitrile (volume ratio 1:1, final HCl concentration 0.05 M) for 24 h; then vacuum dried at room temperature to allow the small molecules to fully physically combine with the graphene sheet, and then washed with ethanol and dried in a conventional manner to obtain the pretreated partial redox graphene film; (4) Joule heating is applied to the pretreated partial redox graphene film to complete crosslinking, carbonization, and graphitization, resulting in an interlayer coupled reduced graphene oxide film with a thickness of 100–300 μm, with 200 μm being a representative example; Figure 2 The figure shows the current / voltage-time curves during Joule heating, exhibiting four voltage drop stages corresponding to dehydration, covalent bonding, deoxygenation and denitrification, and stepwise graphitization. By applying current incrementally, the temperature is gradually increased, allowing specific reactions to occur selectively at each stage. Experimentally, the current is kept constant at each stage, during which a voltage drop is typically observed, indicating structural repair or transformation within the film. The current is maintained for a sufficient time until the voltage reaches a plateau, indicating the end of structural modification at that current, after which the current is further increased. When further increasing the current no longer results in a voltage drop but rather a proportional increase in voltage with the current, it indicates that the film structure has been fully restored, at which point Joule heating is terminated.

[0043] Figure 3 This document illustrates the preparation method and characterization of the interlayer coupled reduced graphene oxide (rGO) film of the present invention, including: (a) a schematic diagram of the film preparation process and structural evolution: starting from a partially reduced rGO film, covalent aromatic ether bonds are formed through a nucleophilic aromatic substitution reaction, followed by carbonization and graphitization treatment to obtain a high-quality reduced graphene oxide structure with interlayer coupling effect; (b) a photograph of a large-area, 200 μm thick interlayer coupled rGO film; and (c) an optical photograph of the prototype device, and an infrared thermal image of the chip surface temperature distribution when using different thermally conductive materials.

[0044] A 10 μm thick blade-coated GO film was characterized to confirm the presence of oxygen-containing functional groups and to determine the degree of oxidation. (Solid state) 13 The 12000-2000 ppm nuclear magnetic resonance (NMR) spectrum showed five distinct peaks, corresponding to carbonyl, carboxyl, and sp groups, respectively. 2 Carbon, hydroxyl, and epoxy groups (arranged in descending order of chemical shift); X-ray photoelectron spectroscopy (XPS) analysis of the C 1s region further confirmed the presence of a large number of oxygen-containing groups, and quantitative analysis of the full spectrum showed that the C:O atomic ratio was approximately 2.1.

[0045] XPS and solid-state NMR analyses confirmed that chemical reduction of the GO film using hydroiodic acid (HI) effectively converted epoxy groups into hydroxyl groups, while significantly reducing the total oxygen content; under 7-hour reduction conditions, the C:O atomic ratio increased to 16.1. After this partial reduction, the interlayer spacing decreased from 0.892 nm to 0.360 nm, indicating that oxygen-containing functional groups were effectively removed and the graphite structure was partially restored. A small amount of hydroxyl groups remained at this stage, serving as reaction sites for subsequent interlayer crosslinking. This crosslinking resulted in a slight increase in the main stacking order and the appearance of a secondary peak corresponding to a 0.684 nm extended interlayer spacing.

[0046] Figure 4 Morphology and structure characterization of ultrathick reduced graphene oxide (rGO) films with interlayer coupling were performed and compared with initial partially reduced rGO films and control films without interlayer coupling. (a) High-resolution X-ray photoelectron spectroscopy (XPS) C1s spectra of the three samples; (b) X-ray diffraction (XRD) patterns; (c) Raman spectra; (d) Scanning electron microscopy (SEM) cross-sectional images of the interlayer coupled ultrathick films; (e) Raman mapping of the films in a 4×4 mm² region; (f) Sheet resistivity measured in regions of different sizes.

[0047] Thick rGO films were immersed in a solution of 1,2,4,5-benzenetetracarbonyl nitrile, washed, and dried, followed by stepwise Joule heating. Covalent aryl ether bonds formed under low current, as evidenced by a significant decrease in the signal intensity of the XPS N 1s spectrum; the XPS O 1s signal also weakened, indicating partial reduction of the oxygen-containing groups, a conclusion further confirmed by the decrease in the intensity of the D peak in the Raman spectrum. X-ray diffraction (XRD) patterns of the samples showed a slight broadening of the characteristic peaks of graphene interlayer stacking, while a new basal plane diffraction peak appeared at an interlayer spacing of 0.684 nm. This is attributed to interlayer crosslinking at residual oxygen-containing sites, resulting from the molecule's planar intercalation within the graphene layers and its stability maintained through π-π interactions. These experimental results fully demonstrate that low-current Joule heating can promote the SNAr reaction between the electrophilic cyanobenzene ring and the hydroxyl groups on the graphene, forming aryl ether bridges connecting adjacent sheets while maintaining the planar alignment of the sheets.

[0048] Under higher Joule thermal currents, oxygen and nitrogen are largely removed. XRD patterns of the films after high-current treatment show the disappearance of low-angle peaks, and the basal interplanar spacing of the graphene stack decreases to 0.341 nm, highly similar to the basal interplanar spacing of natural graphite (0.335 nm), indicating that high-current heating induces significant carbonization and restoration of the in-plane structure. Although the basal diffraction peaks are sharp and intense, low-angle tails remain, indicating that a small amount of interlayer material remains in the localized regions where covalent coupling occurs, resulting in slight inhomogeneity in the interlayer spacing. Using the Scherrer equation and the (00l) diffraction peak, the stacking coherence length of the interlayer-coupled rGO film along the out-of-plane direction is calculated to be 30.5 nm, compared to 18.4 nm for the control group rGO film. This significantly increased coherence length indicates that covalent coupling improves the interlayer arrangement and stacking order of the graphene. XPS full spectrum further confirmed that the characteristic signals of oxygen and nitrogen disappeared, indicating that they were almost completely removed; only a strong CC / C=C characteristic peak was retained in the high-resolution XPS C 1s spectrum, confirming that the aryl ether bond was converted into a carbon-carbon bond, and the observed redshift of the CC / C=C binding energy was related to the sp 2 The hybridization was restored to the characteristic of conjugated double bonds. The carbon-oxygen atomic ratio was measured to be approximately 10⁸. Raman spectroscopy also supports this conclusion, with a significantly suppressed D peak, a strongly enhanced G peak, and a clear 2D peak, all indicating that the graphene lattice possesses high order. The restoration of the in-plane structure and stable interlayer coupling together form a densely packed thin film structure, which is confirmed by cross-sectional scanning electron microscopy (SEM) images, and this structure is comparable to the initial 10 μm thick film. The density of the prepared film is 1.85 g·cm³. -3 The 200 μm thick film contains approximately 597,000 stacked layers. While the control group film without interlayer coupling exhibits a similar C / C=C binding energy, it shows a slightly smaller XRD basal plane spacing, a lower D peak in the Raman spectrum, and obvious interlayer voids or delamination, indicating less interlayer material and weaker interlayer coupling. In summary, the experimental results demonstrate that the prepared film possesses highly graphitized characteristics and forms moderate but stable covalent interlayer crosslinks.

[0049] To evaluate the microstructure and uniformity of the ultrathick rGO film, Raman imaging was first performed in a 4×4 mm² region. Figure 4 e), the results showed that the Raman signal contrast of the film was highly uniform; Raman spectra were collected at 10 random locations within a larger 8×8 cm² area, and the spectra were almost indistinguishable, all showing sharp and strong G peaks (~1580 cm⁻¹) and 2D peaks (~2700 cm⁻¹), confirming that the graphitization degree of the entire film was uniform. Figure 8The in-plane electrical uniformity of the thin film was evaluated using the standard van der Bauer method. The conductivity measured in multiple regions of different sizes remained stable at 4552 S•cm⁻¹ (corresponding to a sheet resistance of 0.011 ± 0.010 Ω•sq⁻¹). Figure 4 f) indicates that the thin film possesses excellent electrical uniformity. This uniform microstructure and continuous conductive pathways ensure efficient and uniform heat transfer.

[0050] Comparison Example The control group graphene film did not contain 1,2,4,5-benzenetetracarbonyl nitrile, that is, step (3) of Example 1 was omitted. Joule heating was directly applied to part of the redox graphene film to complete carbonization and graphitization, and interlayer coupled reduced graphene oxide film was obtained.

[0051] Example 2 Referring to Example 1, 1,2,4,5-benzenetetracarbonyl nitrile is replaced with butadionitrile, and the rest are the same.

[0052] Refer to Example 1, except that hydrochloric acid is omitted, and everything else is the same.

[0053] Figure 5 High-resolution XPS N 1s spectra of crosslinked rGO films with and without HCl and under aliphatic nitrile conditions were obtained. The comparative experiments were all carried out on 10 μm thick rGO films. The results showed that no increase in out-of-plane thermal conductivity was observed under all oxidation degrees when using aliphatic nitrile or when no HCl was added to the DMF solution.

[0054] Example 3 Referring to Example 1, a 10 μm GO film was used, and the chemical reduction was carried out for 1 hour, 3 hours, 7 hours, or 12 hours. Figure 6 XPS full spectrum and high-resolution C1s spectrum of 10 μm thick GO film and partially reduced GO film after chemical reduction for 1 h, 3 h, 7 h and 12 h.

[0055] Test Implementation Examples The interlayer coupled reduced graphene oxide film prepared in Example 1 has a thickness of 200 μm.

[0056] Figure 7 These are low-magnification and high-magnification cross-sectional SEM images of this representative ultra-thick rGO film.

[0057] Figure 8 To demonstrate that the degree of graphitization is consistent with the structural homogeneity, Raman spectra were collected from 10 randomly selected points on the interlayer coupled ultrathick rGO film.

[0058] Figure 9The stress-strain curves of the interlayer coupled ultrathick rGO film are shown to demonstrate its mechanical properties. The tensile strength of the ultrathick rGO film reaches 1.35±0.09 GPa.

[0059] Figure 10 To demonstrate the flexibility and adhesion of the ultra-thick interlayer coupled rGO film; (a) SEM images of the cross-section of the ultra-thick interlayer coupled rGO film after repeated bending (5 cycles), compared with the control rGO film after 5 bending cycles and the commercially available graphitized polyimide film after 2 bending cycles; the ultra-thick interlayer coupled rGO film can be attached to (b) the planar surface of a portable hard drive and (c) the surface of a CPU with sharp edges in operation. The interlayer coupled rGO film maintains structural integrity after bending, can conformally contact with hot surfaces and achieve uniform thermal diffusion, while the control rGO film and the commercially available high-performance graphitized PI show cracks. Table 1 shows the thermal diffusivity, density and specific heat capacity values ​​of a representative 200 μm thick film, which are significantly better than the control rGO film and the commercially available high-performance graphitized PI. Prior art suggests that compared to thin graphene paper (below 5 μm), increased thickness naturally reduces flexibility, but the ultra-thick film prepared in this invention can still withstand significant bending deformation without visible cracks or delamination. This flexibility allows it to conformally contact flat, stepped, or sharp-edged substrates commonly found in thermal interfaces and thermal diffusion applications. The combination of mechanical stability and flexibility ensures its reliable performance in practical thermal management applications.

[0060] The thermal transport performance of the thin film in the in-plane and out-of-plane directions was evaluated using the laser scintillation method. Thermal conductivity (κ, W•m⁻¹•K⁻¹) was calculated using the formula κ=ρ•Cp•α, where ρ is the density (kg•m⁻³), Cp is the specific heat capacity (J•kg⁻¹•K⁻¹), and α is the thermal diffusivity (m²•s⁻¹). A representative 200 μm thick interlayer coupled rGO thin film exhibited excellent thermal transport performance, with an in-plane thermal conductivity of 1465±63 W•m⁻¹•K⁻¹ and an out-of-plane thermal conductivity of 14.0±1.2 W•m⁻¹•K⁻¹. Figure 11 a). In contrast, the in-plane thermal conductivity of the control group film without interlayer coupling was 1307±54 W•m⁻¹•K⁻¹, but its out-of-plane thermal conductivity was significantly lower (2.6±0.7 W•m⁻¹•K⁻¹). This demonstrates that interlayer coupling increased the out-of-plane thermal conductivity of the film by 5.4 times while maintaining high in-plane heat transfer performance.

[0061] Previous studies have used techniques such as layer orientation and high-temperature graphitization to prepare graphene-based films with high in-plane thermal conductivity (1000–1500 W•m⁻¹•K⁻¹), but their out-of-plane thermal conductivity is typically below 5 W•m⁻¹•K⁻¹. Although various strategies exist to enhance interlayer coupling and improve out-of-plane heat transfer, these methods often sacrifice in-plane thermal performance. For example, while commercially available graphitized polyimide films and pyrolytic graphite films can achieve in-plane thermal conductivity of 1000–1500 W•m⁻¹•K⁻¹, their out-of-plane thermal conductivity is usually limited to 2–8 W•m⁻¹•K⁻¹. Metals have a three-dimensional crystal structure, and heat transfer is mainly mediated by free electrons, exhibiting relatively isotropic thermal conduction; however, their thermal conductivity rarely exceeds several hundred watts per meter Kelvin. Figure 11 Tables e and 2 provide a comprehensive comparison of the thermal properties of various materials, highlighting the advantages of the interlayer coupled rGO thin film of this invention: it achieves both high in-plane thermal conductivity and significantly improved out-of-plane thermal conductivity in an ultra-thick structure, providing a highly promising solution for advanced thermal management applications.

[0062] Existing technology suggests that in most heat-transferring crystalline materials, thermal conductivity typically decreases with increasing temperature, following an inverse relationship. This is due to enhanced phonon backscattering at high temperatures. In graphene-based films, structural disorder, defects, and limited lateral sheet dimensions effectively lower the Debye temperature, resulting in significant backscattering even near room temperature. Therefore, thermal conductivity typically decreases rapidly upon heating. Unexpectedly, the interlayer coupled rGO film of this invention exhibits good thermal stability under actual thermal loads. When the temperature increases from 25°C to 250°C, the 200 μm thick film still maintains an in-plane thermal conductivity of 1274 W•m⁻¹•K⁻¹ and an out-of-plane thermal conductivity of 10.8 W•m⁻¹•K⁻¹. Figure 11 (b) represents 87.0% and 77.1% of the room temperature values, respectively. In contrast, the control group film without interlayer coupling under the same conditions retains only 80.2% and 53.8% of the room temperature values ​​for in-plane and out-of-plane thermal conductivity, respectively. Given that the typical operating temperature of high-power electronic components such as CPUs, power integrated circuits, insulated-gate bipolar transistors, and light-emitting diodes is 80–150 °C, the film prepared in this invention maintains high thermal conductivity within this temperature range, highlighting its great potential as a thermal management material for next-generation advanced electronic systems.

[0063] Furthermore, rGO films with different oxidation degrees were prepared by adjusting the reduction time. Figure 11c. Using a representative film thickness of 100 μm, the decrease in out-of-plane thermal conductivity at high reduction levels is due to insufficient surface functional groups required for interlayer coupling. Therefore, the thermal conductivity of the highly reduced film is similar to that of the control group sample without crosslinking agent. Regardless of the initial oxidation level, the in-plane and out-of-plane thermal conductivity of the control group sample are similar.

[0064] In practical applications, efficient thermal management requires both high thermal conductivity and sufficient film thickness to effectively dissipate the high heat flux density, which can reach 1000 W•cm⁻², under extreme conditions. Therefore, high thickness and good thermal conductivity are more suitable indicators for practical applications. In many reported graphene-based films, increasing the thickness often leads to a significant decrease in thermal conductivity. In contrast, the interlayer coupled rGO film of this invention maintains excellent heat transfer performance even at large thicknesses. Figure 11 As shown in Figure d, the in-plane and out-of-plane thermal conductivity of the film with a thickness increased to 300 μm are 1442±45 W•m⁻¹•K⁻¹ and 13.8±1.1 W•m⁻¹•K⁻¹, respectively, which are 91.0% and 90.8% of the values ​​corresponding to the 100 μm thick sample. This retention rate is much higher than that of the control film under the same conditions (80.2% and 78.1%, respectively), and superior to most reported graphene-based materials. Figure 11 f). The thermal conductivity (thermal conductivity × thickness) of the film reaches 0.433 W•K⁻¹, ranking among the highest reported values ​​for graphene-based systems and exceeding that of many commercially available flexible heat-diffusing materials. Furthermore, these thick films retain essentially their thermal conductivity at temperatures up to 250°C, with 86.0% and 74.0% of their in-plane and out-of-plane properties retained, respectively. This is significantly higher than the control group films without interlayer coupling (which retain only 76.2% and 52.0%, respectively). Figure 11 (b. Dashed line).

[0065] In the assembly process of this invention, layer stacking promotes close contact between sub-films, reduces interfacial gaps, and does not disrupt their pre-formed in-plane orientation. Subsequent covalent interlayer coupling forms stable chemical bridges, promoting efficient phonon transport between interfaces. Finally, Joule heating achieves uniform volumetric heating across the entire film thickness, enabling in-situ structural reorganization and defect repair that are difficult to achieve with traditional surface-dominated heat treatment. Therefore, the film thickness can be increased to approximately 300 μm without a significant decrease in phonon transport efficiency. This invention overcomes the problem in existing technologies where increased thickness and temperature lead to a significant decrease in thermal conductivity, extending film thickness to the hundreds of micrometers level, especially at temperatures up to 250°C, while maintaining high thermal conductivity.

[0066] Based on its excellent in-plane and out-of-plane thermal conductivity, this invention evaluates the bulk heat transfer capability of interlayer coupled rGO films: the film is covered on a graphite rod heat source (10 mm in diameter), and the temperature of the other side of the film surface is monitored. During heating, the temperature of the interlayer coupled rGO film rises rapidly, and the temperature distribution across the entire surface is highly uniform, indicating that the heat in localized hot zones is efficiently dissipated. Figure 12 a) In contrast, commercial graphitized polyimide films and the control group rGO films without interlayer coupling exhibit delayed temperature responses, indicating limited heat transfer through film thickness. Furthermore, graphitized polyimide films and copper foils, commonly used as thermal performance benchmarks, both show significant radial temperature gradients, indicating insufficient lateral thermal conductivity. Infrared thermal imaging results confirm that the interlayer-coupled rGO films not only reduce the temperature of hot zones but also achieve a more uniform heat distribution. This performance is attributed to the stable interlayer coupling between graphene layers, which promotes multidirectional phonon transport, enabling the film to rapidly reach thermal equilibrium in both in-plane and out-of-plane directions.

[0067] To evaluate the heat dissipation capability of the thin film in practical applications, an interdigitated chip was used as the heat source, and the interlayer coupled rGO thin film was applied to the test device. Figure 3 c). The generated power was calculated using the formula P=V×I (V is the applied voltage, I is the current), and the corresponding heat flux density of the hot zone (A is the area of ​​the hot zone) was determined using Q=P / A. Each thin film sample was placed between the chip hot zone and the aluminum heat sink to simulate actual thermal interface conditions. Thermal grease was applied to the interface to minimize contact resistance, and the heat dissipation effect of each material was evaluated by monitoring the electrode temperature. After working for 20 seconds at a heat flux density of 1200 W•cm⁻², the temperature of the bare electrode reached 177℃; when using copper foil, graphitized polyimide film, control group rGO film, and interlayer coupled rGO film, the temperature decreased by 40℃, 70℃, 77℃, and 110℃, respectively. Figure 12 b). The corresponding infrared thermal imaging shows that the interlayer coupled rGO film not only suppresses the temperature rise in the hot zone but also promotes uniform heat distribution. The film's heat dissipation performance under long-term operation was tested to further evaluate its practical application potential: Notably, the rGO film maintained stable heat dissipation performance during 20 days of continuous testing. Figure 12 c), and exhibited high durability in 100 on-off thermal cycles (300 s on, 12 s off). Figure 12 (d) This demonstrates its excellent long-term thermal reliability under high power density conditions.

[0068] Table 1. Thermal conductivity parameters of the film of the present invention, the control film, and the commercially available graphitized PI film.

[0069] Compared with other graphene heat dissipation films, the present invention has good thermal conductivity, especially significantly high out-of-plane thermal conductivity. A comparison of some existing products with the present invention is shown in Table 2.

[0070] Table 2 Performance comparison of the product of this invention with existing thermal conductive films

[0071] Application Examples Copper foil is wrapped around both ends of the rGO film as electrodes, and then a 20-micron-thick polyimide is encapsulated on the outside to ensure the insulation and durability of the electrothermal device, which is a conventional technology.

[0072] The interlayer coupled rGO thin film of this invention provides an efficient electron and phonon transport path, thus exhibiting excellent electrothermal performance: its high in-plane and out-of-plane thermal conductivity minimizes the internal temperature gradient, ensuring uniform Joule heating; the continuous conductive network enables rapid conversion of electrical energy into lattice vibrations; combined with its low heat capacity and thin structure, the film exhibits an ultrafast thermal response. This invention fabricated a flexible heater (8 × 4 cm², 200 μm thick) using the rGO thin film, connected a copper electrode to a DC power supply, and characterized its performance using real-time infrared thermal imaging. By adjusting the applied voltage between 0.7 and 1.9 V (corresponding to a power density of 1000–7000 W·m⁻²), the film temperature can be precisely and reversibly controlled. Figure 13 ab). When a voltage of 1.9 V is applied, the film temperature rises rapidly from 26 °C to 227 °C in 3.5 s, with a heating rate of 56.8 °C·s⁻¹, which is significantly faster than the reported rGO or chemical vapor deposition (CVD) graphene heaters (typically 20~30 °C·s⁻¹).

[0073] The temperature difference of the 8×4 cm² film is maintained below 5 ℃. Figure 13 (See illustration b), demonstrating excellent heating uniformity. The device maintains stable performance even after repeated bending and flattening during continuous operation. Figure 13 c), and exhibited high durability in 100 on / off cycles (20 s on, 10 s off). Figure 14 In de-icing tests, the rGO film melted a 10 mm thick ice layer within 168 s (rate 16.8 s·mm⁻¹), outperforming commercial nickel-chromium heating films (272 s, 27.2 s·mm⁻¹). Figure 13(de) Energy savings of approximately 40%. The energy consumption per unit ice layer thickness of the interlayer-coupled rGO film is approximately 0.032 kWh·mm⁻¹·m⁻² (13f), significantly lower than the control group rGO film without interlayer coupling (0.042 kWh·mm⁻¹·m⁻²) and commercial nickel-chromium heaters (approximately 0.053 kWh·mm⁻¹·m⁻²). Overall, the enhanced interlayer coupling minimizes Joule heating losses, promotes efficient multidirectional heat transfer, and enables a fast, durable, and energy-efficient operating mode, demonstrating the potential of rGO films in advanced thermal management applications.

[0074] From a practical application perspective, the strategy of this invention has significant potential for large-scale, low-cost fabrication: the blade coating process used to prepare the film is suitable for large-area manufacturing and can be easily applied to continuous processing flows such as roll-to-roll coating; the Joule heating process that induces interlayer coupling can be applied to large-area films and can theoretically be integrated into continuous or roll-to-roll production lines. Regarding production costs, this process is based on solution-processable graphene films and does not require prolonged high-temperature furnace annealing, thus resulting in lower energy consumption and overall lower processing costs compared to traditional heat treatment. Although further optimization is needed to improve production efficiency and ensure thickness and performance uniformity at an industrial scale, this strategy provides a highly promising approach for the large-scale fabrication of ultra-thick, high-performance graphene films for practical thermal management.

[0075] Early studies on graphene laminates and reduced graphene oxide films showed that macroscopic graphene-based films could be used for heat transfer, but their thermal conductivity exhibited strong anisotropy, limiting their out-of-plane performance. To address these issues, researchers employed pressure-assisted stacking to reduce interlayer porosity, enhanced π-π interactions through high-temperature annealing, and further improved interlayer coupling by incorporating metal ions, thermal bridges, or nanofillers such as carbon nanotubes and boron nitride nanosheets. Some studies have also reported that vertically aligned graphene structures can promote out-of-plane heat transfer. However, these methods often disrupt in-plane phonon transport paths, impairing lateral heat transfer performance. Therefore, achieving stable, simultaneous high thermal conductivity in both in-plane and out-of-plane directions (especially in ultrathick graphene films) remains a significant unsolved challenge in the development of efficient, multifunctional thermal management materials. This invention introduces 1,2,4,5-tetracyanobenzene, which, through thermal deoxidation and graphitization, enhances planar cross-linking and improves in-plane conjugation, resulting in films with excellent heat transfer performance in both directions. As an example, a representative rGO film with a thickness of approximately 200 μm was prepared, achieving in-plane and out-of-plane thermal conductivity of 1465 ± 63 W·m, respectively. -1 ·K -1 and 14.0±1.2 W·m -1 ·K -1This superior performance is maintained even at thicker films (up to 300 μm) and high temperatures of 250 °C, highlighting the stability of interlayer coupling in ultrathick graphene assemblies. At 1200 W·cm⁻¹ -2 At a localized heat flux density, a 200 μm thick film can reduce the surface temperature by 110°C within 20 seconds, demonstrating rapid and efficient heat diffusion capabilities. In addition to passive heat conduction, this film can also achieve rapid, uniform, and voltage-adjustable electrothermal heating, while exhibiting excellent stability and mechanical strength. This scalable strategy for constructing covalently bridged graphene films provides a general platform for advanced thermal management and energy-efficient electrothermal devices.

Claims

1. A method for preparing interlayer coupled reduced graphene oxide thin films, characterized in that, The process includes the following steps: impregnating a portion of a reduced graphene oxide film with a cyanobenzene compound solution, followed by crosslinking, carbonization, and graphitization to obtain an interlayer coupled reduced graphene oxide film.

2. The method for preparing interlayer coupled reduced graphene oxide thin film according to claim 1, characterized in that, Crosslinking reaction is carried out by Joule heating, followed by carbonization and graphitization to obtain interlayer coupled reduced graphene oxide film.

3. The method for preparing interlayer coupled reduced graphene oxide thin film according to claim 1, characterized in that, A partial redox graphene film was obtained by reducing the graphene film using a chemical reduction method.

4. The method for preparing interlayer coupled reduced graphene oxide thin film according to claim 1, characterized in that, The cyanobenzene compound solution includes the cyanobenzene compound, acid, and organic solvent.

5. The interlayer coupled reduced graphene oxide film prepared by the method for preparing interlayer coupled reduced graphene oxide film according to claim 1.

6. The application of the interlayer coupled reduced graphene oxide film of claim 5 in the preparation of conductive and / or thermally conductive materials.

7. The application of the interlayer coupled reduced graphene oxide film according to claim 5 in the preparation of thermally conductive devices.

8. The application of the interlayer coupled reduced graphene oxide film of claim 5 in the preparation of heating devices.

9. A heat-conducting device comprising the interlayer coupled reduced graphene oxide film of claim 5.

10. A heat dissipation device or heating device, comprising the interlayer coupled reduced graphene oxide film as described in claim 5.

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