Nano-inks of carbon nanomaterials for printing and coating

Abstract

To provide electrically conductive ink compositions that comprise carbon nanomaterials of one-dimensional, two-dimensional, and quasi-three-dimensional nanostructures and / or their combinations, and / or doping with elements such as nitrogen, boron, sulfur, in certain ratios.SOLUTION: An ink composition comprising at least one nanomaterial in a certain amount selected from the group consisting of graphene, carbon nanotubes, and graphene aerosol gels.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 866,412, filed June 25, 2019, and U.S. Provisional Patent Application No. 62 / 954,118, filed December 27, 2019, both of which are incorporated by reference herein in their entireties. Statement of Federally Funded Research This invention was made with government support under Grant No. CBET1935676 awarded by the National Science Foundation (NSF). The government has certain rights in this invention. [Background technology]

[0002] FIELD OF THE INVENTION The present invention relates to various electronic-grade ink and / or dispersion formulations comprising, consisting of, or consisting essentially of one-dimensional, two-dimensional, and quasi-three-dimensional nanostructured and / or combinations thereof carbon nanomaterials in specific ratios. These inks can be used in many applications, including, but not limited to, printable and flexible electronics and functional coatings. Preferred applications for these inks are in the areas of energy storage, electrochemical sensing, field-effect transistors, and transparent conductive electrodes. The process is scalable and suitable for large-scale production / manufacturing.

[0003] Description of the Prior Art Rechargeable and microscale energy storage devices, such as micro-supercapacitors (micro-SCs) and micro-batteries, are increasingly in demand for emerging applications such as the Internet of Things (IoT), autonomous ubiquitous sensors, and small appliances, including wearable devices. Based on the principles of electric double layer capacitance (EDLC) and redox-active reactions at the solid-electrolyte interface, energy storage devices possess the properties of charging and discharging. Therefore, reliable charge-discharge cycling constitutes an essential feature of any super / micro-supercapacitor and battery technology. Graphene, with its large surface area (2630 m for an isolated single sheet of graphene), is a promising candidate for a wide range of applications. 2 Graphene has long been sought after for energy storage applications due to its high energy density (EEL / g). However, harnessing its properties in large-scale, scalable platforms along with its thickness tuning has been challenging due to interparticle resistance, mechanical instability, and their correlation. Alternative approaches to combine and mitigate these adverse effects by modifying the physical structure of graphene at the micro / nanoscale (e.g., by increasing the available surface area exposed to the environment) and to exploit the benefits of utilizing higher EDLCs would be beneficial for the development of new technological avenues. Various types of additive manufacturing, such as screen printing, inkjet printing, and 3D printing, have recently been increasingly adopted due to their cost-effectiveness, fabrication simplicity, and wide process compatibility. Therefore, there is a need in the art to be able to print graphene micro-SCs and micro-batteries with engineered surfaces at the micro / nanoscale with higher available surface areas to achieve the above-mentioned next-generation SCs and batteries.

[0004] US Patent Application Publication No. 2017 / 0081537 relates to a rapid and scalable methodology for graphene dispersion and concentration in a polymer-organic solvent medium that can be utilized without centrifugation to enhance graphene concentration.

[0005] International Patent Publication No. 2014 / 210584 relates to dispersions of nanoplatelet graphene-like material, such as graphene nanoplatelets, in solid or liquid dispersions, where the nanoplatelet graphene-like material is substantially uniformly dispersed in the dispersion by a graphene-like material dispersant. Such dispersions can be used to prepare articles by three-dimensional (3D) printing, as well as to provide conductive inks and coatings, chemical and biosensors, electrodes, energy storage devices, solar cells, etc. Liquid dispersions can be prepared, for example, by sonicating a solution of graphite flakes, a dispersant, and a liquid dispersion, while solid dispersions can be prepared, for example, by combining a molten polymer with a liquid dispersion, dissolving a solid polymer in a miscible solvent and then blending it with a liquid dispersion, dissolving a solid polymer in a liquid dispersion, or polymerizing one or more monomers in a liquid dispersion to form a solid polymer.

[0006] U.S. Patent No. 9,440,857 relates to a method for producing pristine graphene particles by one-step, gas-phase, catalyst-free detonation of a mixture of one or more carbon-containing hydrocarbon compounds and one or more oxidants. The detonation reaction occurs very rapidly at relatively high temperatures above 3000 K, producing graphene nanosheets that can be recovered from the reaction vessel, such as in aerosol form. The graphene nanosheets may be stacked, for example, in monolayers, bilayers, or trilayers, and may have an average particle size of about 35 to about 250 nm.

[0007] Each of the foregoing references is incorporated herein by reference in its entirety. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Application Publication No. 2017 / 0081537 [Patent Document 2] International Patent Publication No. 2014 / 210584 [Patent Document 3] U.S. Patent No. 9,440,857 Summary of the Invention [Means for solving the problem]

[0009] In one embodiment, graphene aerosol gel inks have been formulated and used for inkjet printing of micro-supercapacitors. In a specific embodiment, the graphene aerosol gels used were synthesized by controlled environmental detonation of hydrocarbons such as methane, ethylene, and acetylene.

[0010] In another embodiment, there is provided an ink composition comprising a nanomaterial selected from the group consisting of graphene, carbon nanotubes, and graphene aerosol gel. In a preferred embodiment, the ink composition comprises, consists of, or consists essentially of graphene aerosol gel as the primary or only graphene or carbon material.

[0011] According to yet another embodiment of the present invention, there is provided a method of forming an ink composition comprising providing a mixture comprising a graphene aerosol gel and a surfactant, preferably ethyl cellulose or nitrocellulose, dispersed in a liquid vehicle system, the liquid vehicle system preferably comprising a mixture of one or more ketones and one or more alcohols, more preferably a mixture of cyclohexanone and terpineol.

[0012] In another embodiment of the present invention, an ink composition is provided that includes graphene or graphene oxide and a low concentration of a second component, such as carbon nanotubes or graphene aerosol gel, or a combination thereof. The base graphene inks used in the tests described below are commercially available graphene inks and homemade graphene inks. The carbon nanotubes used to make the composite inks are commercially available, and the graphene aerosol gel used in the composite inks is made according to the teachings of U.S. Pat. No. 9,440,857, the entire contents of which are incorporated herein by reference. The carbon nanotubes are multiwalled carbon nanotubes with metallic properties, and the graphene aerosol gel is reduced graphene oxide with a controlled carbon-to-oxygen ratio when synthesized via a hydrocarbon detonation route.

[0013] According to yet another embodiment of the present invention, there is provided a method of forming an ink composition comprising providing a graphene or graphene oxide-containing ink precursor comprising a quantity of graphene or graphene oxide particles dispersed in a liquid vehicle, wherein a quantity of at least one of carbon nanotubes and graphene aerosol gel is dispersed within the ink.

[0014] After incorporating carbon nanotubes and graphene aerosol gel into graphene ink, the resulting nanoink exhibits unique features regarding their structural, electrical, and electrochemical properties. Both the coated surface and the printed patterns were tested on flexible substrates such as polyimide film, and the results were excellent. The superior electronic and electrochemical pathways for the technology make it useful for applications in electronics, sensing, energy, and IoT. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of the production of nanoink according to the present invention. [Figure 2] FIG. 1 is a schematic diagram of a printing technique for fabricating electronic devices using nanoinks in accordance with the present invention. [Figure 3]Schematic representation of the drop-on-demand equipment and printing process used to fabricate electrodes, sensors, circuits, etc. using nanoinks. [Figure 4a] SEM image of a sensor printed using graphene ink. [Figure 4b] 10 is an SEM image of a printed sensor using a composite ink containing graphene and graphene aerosol gel. [Figure 4c] 1 is an SEM image of a sensor printed using a composite ink containing graphene and carbon nanotubes. [Figure 5a] TEM images of the nanostructures of the components and their intermixing at the nanoscale of graphene flakes. [Figure 5c] TEM images of the nanostructures of the components and their intermixing at the nanoscale of the graphene aerosol gel mixed with and covered by graphene. [Figure 5e] TEM images of the nanostructures of the components and their mixture at the nanoscale of carbon nanotubes mixed with and wrapped by graphene. [Figure 5b] High-resolution TEM image of graphene. [Figure 5d] High-resolution TEM image of graphene aerosol gel in intimate contact with graphene. [Figure 5f] High-resolution TEM image of a carbon nanotube in intimate contact with graphene. [Figure 6] 10 is a graph of cyclic voltammetry of three sensors printed with graphene ink, graphene and graphene aerosol gel composite ink, and graphene and carbon nanotube composite ink. [Figure 7] 1 is an image of a printed supercapacitor approximately 10 mm x 8 mm with interdigitated finger-shaped electrodes. [Figure 8]Figure 1 shows a low-resolution transmission electron microscope (TEM) image of graphene aerosol gel ink (left) and its high-resolution (HR) TEM image (right, taken in the square marked area in the left image), showing atomically thin graphene walls in the multilayer graphene aerosol gel. [Figure 9] FIG. 10 is a Raman spectrum of graphene aerosol gel ink. The printed ink was post-treated (controlled environment annealing, described below) and the Raman spectrum was measured using 532 nm excitation. [Figure 10a] 1 is a chart showing the galvanostatic charge-discharge characteristics of a micro-supercapacitor cell for five representative charge and discharge cycles at an early stage. [Figure 10b] 1 is a chart showing the constant current charge and discharge characteristics of a micro-supercapacitor cell for five representative charge and discharge cycles at the end of 10,000 cycles. [Figure 11] 1 illustrates various aspects of the present invention from material and ink formulation to fabrication of energy storage devices. [Figure 12a] Schematic design of inkjet-printed interdigitated micro-supercapacitor. [Figure 12b] Photograph of a resistor element printed on a flexible polyimide substrate. [Figure 12c] High resolution SEM image of inkjet printed fingers; inset shows a higher magnification of one such finger, showing its width and uniformity. [Figure 12d] 10 is an SEM image showing the surface morphology of the printed fingers, showing spherical graphene aerosol gel particles. [Figure 13]Figure 1 shows four consecutive high-resolution TEM measurements for the microstructural characterization of graphene aerosol gels (GAGs). (a) shows an aggregate of graphene nanosheets mounted on a TEM copper grid. (b) shows a higher magnification image of a graphene nanosheet showing higher contrast at the boundary relative to the center of the sheet. (c) shows a high-resolution image of one such nanosheet showing a fringe / stripe-like microstructure at the boundary, with the inset image showing that the stripes are essentially formed by the terminating edges of the graphene sheets. (d) shows the predominance of the stripe-like microstructure present in the ink. [Figure 14a] Photograph showing three micro-supercapacitors printed in series. [Figure 14b] Photograph showing three micro-supercapacitors printed in parallel. DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments of the present invention relate to nanoinks and methods for making such nanoinks, which comprise, consist of, or consist essentially of highly stable suspensions containing hybrid structures of 2D graphene, 1D nanotubes, and / or 3D aerosol gels, all of which are microscopic in size and comprise carbon as the base chemical element. In certain embodiments, various energy storage devices are provided in the form of mechanically flexible supercapacitors (in interdigitated electrode (IDE) configuration) fabricated (printed) from graphene inks and graphene aerosol gel inks on polyimide substrates.

[0017] According to one or more embodiments, an ink composition is provided that includes graphene (including reduced graphene oxide), carbon nanotubes, and / or graphene aerosol gel (GAG), commonly referred to as a "carbon nanomaterial," dispersed in a liquid vehicle. Graphene and / or carbon nanotubes can be prepared according to any technique known in the art. In the case of graphene, high shear forces in a specific solvent type and ratio combination enable exfoliation of the graphite when used in a solvent medium with a specific graphene to solvent concentration. Graphene aerosol gel can be prepared by catalyst-free, electric spark-initiated detonation of an acetylene precursor (C2H2) with a controlled amount of oxygen in a reaction chamber. An exemplary process for producing GAG is described in U.S. Pat. No. 9,440,857. The process described in the '857 patent can be understood as forming a gel via the conversion of acetylene molecules to free carbon atoms or ions, followed by carbon aerosol formation, graphite carbon formation, and a subsequent gelation process.

[0018] In one or more embodiments, the liquid vehicle in which the carbon nanomaterials are dispersed comprises one or more organic compounds compatible with the carbon nanomaterials. In certain embodiments, the liquid vehicle comprises one or more ketones, one or more alcohols, or a mixture of one or more ketones and one or more alcohols. Exemplary ketones that may be used in accordance with the present invention include aliphatic and aromatic cyclic ketones, such as cyclohexanone. Exemplary alcohols that may be used in accordance with the present invention include aliphatic and aromatic alcohols, such as terpineol. In other embodiments, the liquid vehicle may comprise an amide, such as N,N-dimethylformamide (DMF), and / or a lactam, such as N-methyl-2-pyrrolidone (NMP).

[0019] In certain embodiments, the liquid vehicle comprises from about 60% to about 99%, from about 70% to about 95%, or from about 80% to about 90% by weight of one or more ketones, and from about 1% to about 35%, from about 5% to about 30%, or from about 10% to about 20% by weight of one or more alcohols.

[0020] In one or more embodiments, when the carbon nanomaterials include carbon nanotubes and / or graphene aerosol-gel particles, the concentration of these carbon nanomaterials in the ink is about 0.01 to about 10 mg / ml, about 0.05 to about 5 mg / ml, or about 0.1 to about 3.0 mg / ml. In certain embodiments, in addition to CNT and / or GAG particles, the ink composition may further include graphene (including reduced graphene oxide) and / or graphene oxide particles, and / or doped carbon nanomaterials by doping with elements such as nitrogen, sulfur, and boron (FIG. 11). In such embodiments, the concentration of graphene and / or graphene oxide particles is about 1 to about 30 mg / ml, about 5 to about 25 mg / ml, or about 10 to about 15 mg / ml.

[0021] In certain embodiments, the carbon nanomaterials, particularly graphene aerosol gels, have a D90 particle size (90% of the distribution has a smaller particle size and 10% has a larger particle size) of about 0.1 to about 10 μm, about 0.25 to about 7.5 μm, or about 0.45 to about 5 μm.

[0022] The ink composition may further comprise one or more optional ingredients. In one or more embodiments, the ink composition may comprise one or more surfactants that aid in forming a stable suspension of the carbon nanomaterial in the liquid vehicle. Exemplary surfactants that may be used with the present invention include ethyl cellulose, nitrocellulose, sodium dodecyl sulfate (SDS), ethylenediaminetetraacetic acid (EDTA), and sodium dodecylbenzenesulfonate (SDBS). In certain embodiments, the ink composition comprises from about 1 to about 500 mg / ml, from about 2 to about 300 mg / ml, or from about 5 to about 200 mg / ml of one or more surfactants.

[0023] In certain embodiments, the ink composition may have a viscosity of less than 30 cP, less than 25 cP, or less than 20 cP at room temperature (i.e., about 25° C.) so that it is jettable from an inkjet printhead.

[0024] In another embodiment of the present invention, a method for forming a composite ink is provided. Exemplary methods are described in the Examples below. However, generally, composite ink compositions according to the present invention may be formulated via a number of routes. According to one embodiment, a mixture is provided that includes the graphene aerosol gel described herein and one or more surfactants. In certain embodiments, the mixture can be formed by first dispersing a quantity of graphene aerosol gel particles in a liquid medium, such as an organic solvent. In certain embodiments, the organic solvent used can be an alcohol, such as ethyl alcohol. To the GAG ​​dispersion, a quantity of surfactant, such as ethyl cellulose or nitrocellulose, is added. In one or more embodiments, the ratio of GAG to surfactant is 10:1 to 1000:1, 25:1 to 500:1, or 100:1 to 250:1 by weight. The GAG ​​is then dispersed in the solvent using stirring or sonication for a period of time until the GAG ​​particles disintegrate into GAG flakes.

[0025] The smaller GAG flakes are then separated from the suspension, for example, by centrifugation. The GAG ​​flakes in the supernatant may be flocculated to remove excess surfactant. This can be accomplished by preparing an NaCl solution and adding it to the flakes. The resulting suspension can be filtered to recover the flocculated GAG flakes. The resulting flakes can be dried to recover the graphene-surfactant powder. Optionally, larger GAG flakes can be removed from the powder by redispersing the dried powder in an organic solvent and filtering the dispersion. The permeate containing the filtered GAG flakes can be flocculated and dried to form a powder, as in the previous step.

[0026] Finally, a composite ink can be formed by dispersing the GAG ​​flakes and surfactant powder in a liquid vehicle system, as described above, and then agitating the dispersion, such as by using sonication, to form a homogeneous ink composition.

[0027] According to another embodiment of the present invention, a composite ink can be formulated by first providing a graphene or reduced graphene oxide dispersion. An exemplary reduced graphene oxide dispersion can be formed by mixing reduced graphene oxide microparticles with a liquid vehicle system, such as a mixture of cyclohexanone and terpineol, as described above. In certain embodiments, the reduced graphene oxide particles are present in the vehicle system at a concentration of about 1 to about 30 mg / ml, about 5 to about 20 mg / ml, or about 10 to about 15 mg / ml. A certain amount of surfactant may then be added to the mixture at a level of about 0.5 to about 15 mg / ml, about 1 to about 10 mg / ml, or about 3 to about 5 ml. The resulting mixture can be stirred, such as by sonication, under elevated temperatures not exceeding 400°C to form an ink suspension. In one or more embodiments, an amount of CNT or GAG particles may be added to the ink formulation at a level of about 0.01 to about 5 mg / ml, about 0.05 to about 2.5 mg / ml, or about 0.1 to about 1 mg / ml, and the resulting mixture can then be sonicated to form a stable suspension.

[0028] The composite ink can be used to fabricate electronic devices that include one or more traces printed with the ink. In certain embodiments, the ink was printed onto a substrate using a jet printer, although any printing technique capable of producing traces of the desired dimensions could be used. Exemplary electronic devices that can be fabricated with the composite ink include capacitors, supercapacitors, microcapacitors, ultracapacitors, and pseudocapacitors. In certain embodiments, the ink can be used to print electrodes, which, when combined with one or more electrolytes, can be used to fabricate batteries.

[0029] In one or more embodiments, electronic devices may be formed by printing conductive traces onto a substrate using any of the composite inks described herein. In certain embodiments, the substrate used is a flexible substrate formed from a synthetic resin material, such as a polyimide film. However, it is within the scope of the present invention that other types of substrates may be used, including non-flexible substrates, such as rigid plastics, glass, and ceramics. In certain embodiments, once the conductive traces are fabricated, the traces may be annealed. The annealing step may be performed in an inert atmosphere, such as a nitrogen atmosphere, at a temperature of about 200°C to about 500°C, about 300°C to about 450°C, or about 350°C. The annealing step may be performed for a period of about 1 to about 5 hours.

[0030] FIG. 11 illustrates various concepts according to the present invention, starting with the production of carbon nanomaterials through the formulation of nanoinks and composite inks and the fabrication of energy storage devices. The first step involves producing carbon-based nanomaterials from at least one low-dimensional material 40. Exemplary low-dimensional materials are graphite or one or more organic reactants, such as hydrocarbon compounds, that can be used to synthesize nanomaterials. From the low-dimensional material 40, various nanomaterials can be produced, such as one-dimensional carbon nanotubes 42, two-dimensional graphene and graphene oxide sheets 44, quasi-three-dimensional graphene aerosol gels 46, or various doped carbon nanomaterials 48. Doped carbon nanomaterials may include, for example, any of the nanomaterials 42, 44, or 46 that further include nitrogen, boron, or sulfur atoms as dopants.

[0031] The nanomaterials 42, 44, 46, 48 can then be used to formulate nanoinks and composite nanoinks 50. The nanoinks 50 can then be used in the fabrication of various energy storage devices, such as printed electrodes 52 from which supercapacitors 54 and pseudocapacitors 56 can be fabricated. The printed electrodes 52 can also be used with one or more electrolytes 58 to construct batteries 60. [Example]

[0032] The following examples describe various embodiments of the present invention, particularly ink compositions containing graphene, reduced graphene oxide, and graphene aerosol gel. They are intended to illustrate certain concepts that may be used with the present invention and should not be construed as limiting its overall scope. In certain embodiments, nanoink formulations may begin with commercially available graphene inks, such as those available from Sigma-Aldrich. However, as described below, carbon-containing nanomaterials can be synthesized and formulated into composite ink compositions.

[0033] FIG. 1 schematically illustrates a process for making two graphene-containing inks according to one embodiment of the present invention. In both processes, graphene ink 10 is used as the base formulation. In one process, graphene aerosol gel is added to the graphene ink base to form graphene aerosol gel ink 12, which contains both graphene 14 and graphene aerosol gel particles 16. In the second process, carbon nanotubes are added to graphene ink 10 to form graphene-carbon nanotube ink 18, which contains both graphene 14 and carbon nanotubes 20. Note that the carbon nanotubes may include single-walled or multi-walled carbon nanotubes. As shown in FIG. 2, the ink can then be used to fabricate electronic devices 22, such as electrodes, by printing ink 24 from inkjet head 26 onto a plastic substrate 28 in a desired configuration.

[0034] [Example 1] Reduced graphene oxide ink The reduced graphene oxide ink can be formed using the following steps.

[0035] 1. 85% by volume of cyclohexanone (Sigma Aldrich) was mixed with 15% by volume of terpineol (Sigma Aldrich) to create a homogeneous solvent mixture. This solvent mixture forms the vehicle for the ink formulation.

[0036] 2. The solvent was mixed with reduced graphene oxide (ACS Materials) at a ratio of 10-15 mg / mL. Alternatively, commercially available graphene powder (e.g., available from Graphene Supermarket) can be used.

[0037] 3. 3-5 mg / mL of ethyl cellulose was added to the mixture (ethyl cellulose from Sigma Aldrich).

[0038] 4. The mixture was treated in an ultrasonic bath overnight at a temperature not exceeding 400°C.

[0039] 5. The mixture was probe sonicated for 60 minutes with 15 minute steps and 15 minute rest periods between steps, with the probe sonicator set at 30% power. Steps were taken to ensure the temperature did not exceed 400°C.

[0040] 6. The ink / suspension is sonicated for a further 10 minutes, followed by vortex mixing for approximately 5 minutes before printing.

[0041] Additionally, for composite nanoink formulations containing carbon nanotubes and / or graphene aerosol gels, the following steps are also performed.

[0042] 7. Mix 0.3 mg / mL of nanotube or graphene aerosol gel with the graphene ink and subject the resulting ink to ultrasonic bath treatment for 1 hour.

[0043] The formulated composite inks containing graphene nanosheets and carbon nanotubes (CNTs), as well as the formulated composite inks containing graphene nanosheets and graphene aerosol gel (GAG), were then used in a material printer (SonoPlot Microplotter II) to fabricate printed electrodes (on flexible and bendable substrates such as polyimide) for characterization of their electrochemical properties. After the printing process, the electrodes were annealed at 300 °C for 2 h in a nitrogen atmosphere. The printed electrodes were tested using a standard hexaamine ruthenium(III) chloride solution as an electrochemical probe. To understand the electron transfer (or charge transfer) process between the nanomaterial surface and the solution sample through electrochemical methods, cyclic voltammetry (CV) tests were performed, in which a voltage was swept across the electrode relative to a standard Ag / AgCl reference potential, and oxidation and reduction currents were monitored. The oxidation and reduction active surface when the voltage was swept back and forth is an indication of charge transfer and indicates the electroactivity of the surface. Electrodes (i.e., printed electrodes) fabricated by additive manufacturing of the composite inks described above were characterized using this technique. Both composite inks demonstrated significantly active electrochemical signals (one order of magnitude higher), demonstrating the role of carbon nanotubes and graphene aerosol gel additives in graphene inks for fabricating sensors and energy storage devices. This characteristic is attributed to the porous structure of the added nanomaterials, which can provide a larger effective reactive surface area. The porous structure and network distribution of the GAG ​​and CNT matrices were confirmed by transmission electron microscopy (TEM) images.

[0044] Figure 3 shows a schematic of a drop-on-demand and printing process that can be used to fabricate graphene electronics, such as electrodes, sensors, and circuits. Ink 30 is ejected from an inkjet head 32 and deposited onto a plastic substrate 34, which is placed on a printer plate 36. The electrochemical and charge transfer properties of strip electrodes 38 formed with each ink were tested.

[0045] Figures 4a-c show the surface microstructure of the printed sensors, measured using scanning electron microscope imaging (SEM). The three sensors comprise, consist of, or consist essentially of (a) graphene, (b) a composite of graphene and graphene aerosol gel, and (c) a composite of graphene and carbon nanotubes. Isolated and / or smaller clusters of graphene aerosol gel and individual carbon nanotubes are shown intimately connected with the host graphene flakes, providing additional surface properties as evidenced by electrochemical activity, as described below. The density of the aerosol gel and carbon nanotubes was intentionally kept small to avoid aggregation of the nanostructures, which could adversely affect their functionality.

[0046] Figures 5a-5d are TEM images showing the nanostructures of the components and their blending at the nanoscale in the three inks. Figures 5a, 5c, and 5e show TEM images of graphene flakes, graphene aerosol gel mixed with and covered by graphene, and carbon nanotubes mixed with and covered by graphene, respectively. Figures 5b, 5d, and 5f show high-resolution images of graphene, graphene aerosol gel in intimate contact with graphene, and carbon nanotubes (<10 nm) in intimate contact with graphene.

[0047] Raman spectra were obtained for the printed sensors, which were printed by one-pass printing using inks containing (a) graphene, (b) graphene composite with graphene aerosol gel, and (c) graphene composite with carbon nanotubes. The characteristic D peak, G peak, and 2D peak were observed at approximately 1350 cm. -1 , 1580cm -1 , and 2700 cm -1 , indicating the presence of intact molecular and structural vibrational modes of carbon nanomaterials.

[0048] Figure 6 shows graphs of cyclic voltammetry for three printed sensors fabricated using inks containing graphene (a), graphene composite with graphene aerosol gel (b), and graphene composite with CNTs (c). The sensors were tested with a standard Ag / AgCl reference electrode and a standard hexaammineruthenium(III) chloride redox probe. When the graphene ink contained graphene aerosol gel or carbon nanotube additives, very clear and symmetrical oxidation and reduction peaks were observed, indicating improved electroactive properties of the composite ink. The cathodic and anodic currents were orders of magnitude higher for the composite ink compared to the graphene ink. The graphene ink still exhibited weak interactions with the redox probe.

[0049] Cyclic voltammetry of printed sensors containing graphene composite with graphene aerosol-gel ink and graphene composite with CNT ink was analyzed at scan rates of 5 mV / s, 10 mV / s, 25 mV / s, 50 mV / s, and 100 mV / s. Graphs showing the linear anodic and cathodic characteristics of these two sensors were also generated. While both types exhibit high electrochemical electron transfer, the sensor containing the carbon nanotube additive performed slightly better than the sensor containing the graphene aerosol-gel additive.

[0050] Cyclic voltammetry was also measured for the composite graphene-graphene aerosol gel and composite graphene-carbon nanotube sensors, respectively, at 5.0 mM glucose in 0.1 M NaOH at various scan rates. Graphs showing the corresponding linear cathodic and anodic peak current positions were also generated, indicating that the sensors printed or coated with the composite graphene ink could be used for glucose sensing.

[0051] [Example 2] Formulation of graphene ink from graphite powder In another embodiment, the graphene aerosol gel ink may be formulated as follows:

[0052] 1. First, 1.5 mg / ml ethyl cellulose (viscosity 4 cP) (i.e., 0.25 g) was dispersed in 50 ml ethanol and treated in an ultrasonic bath. Then, 50 mg / ml graphite (ACS Materials) (i.e., 2.5 g) was added to the mixture.

[0053] 2. The dispersion was probe sonicated in a probe apparatus for 3 hours at a set energy of 50% (5 seconds ON followed by 5 seconds OFF, while the beaker containing the mixture was kept in an ice bath).

[0054] 3. The dispersion was centrifuged at 10,000 g (11641 rpm) for 15 minutes, after which the supernatant was collected.

[0055] 4. The supernatant was mixed with 0.04 g / ml NaCl in a volume ratio of 1:2, and then heat-treated on a hot plate at 50°C with stirring using a magnetizer for 5 minutes.

[0056] 5. To recover the powder free of residual salt, the graphene / EC solid was washed with deionized water, isolated by vacuum, and then placed back on the hot plate to dry.

[0057] 6. Redisperse the graphene / EC powder in ethanol and filter through a 5 μm filter pore size.

[0058] 7. The dispersion was mixed again with 0.04 g / ml NaCl in a volume ratio of 1:2, followed by stirring with a magnetizer on a hot plate for 5 minutes.

[0059] 8. To recover the final powder free of residual salts, the graphene / EC solid was washed with deionized water and isolated by a vacuum filtration process. Finally, the product was placed on a hot plate to dry.

[0060] 9. Finally, this powder is used at a concentration of 50-200 mg / mL in a mixture of 85% by volume cyclohexanone (Sigma Aldrich) and 15% by volume terpineol (Sigma Aldrich) to create a homogeneous solvent mixture.

[0061] [Example 3] Graphene aerosol gel ink formulation In another embodiment, the graphene aerosol gel ink may be formulated as follows:

[0062] The following chemicals can be used: a. Solvent: Ethyl alcohol b. Surfactant: Ethyl cellulose (product number 200646, Sigma Aldrich, 4 cp, 5% in toluene / ethanol (80:20 (liters)). c. Graphene aerosol gel: (O2 / C2H2) ratio = 0.5.

[0063] Step 1. Suspend graphene aerosol gel in a solvent. a. Pour 50 ml of ethyl alcohol into a clean glass container using a calibrated measuring cylinder and add 250 mg of graphene aerosol gel (i.e., at a concentration of 5 mg / ml). Shake gently for 10-15 minutes. b. Add 1.25 g of ethyl cellulose (i.e., at a concentration of 25 mg / ml). c. Disperse the graphene aerosol gel in the solvent using probe sonication with a 5 second pulse on time and a 5 second pulse off time while maintaining the temperature in an ice bath at 50% wattage setting for 1 hour. After this step, the graphene aerosol gel disintegrates into graphene aerosol gel flakes.

[0064] Step 2. Separation of smaller graphene aerosol gel flakes. d. Centrifuge the suspension for 15 minutes using a speed equivalent to 11,000 rpm (10,000 rcf). Gently decant the liquid from the top of the centrifuge vial and collect it in a beaker.

[0065] Step 3. Flocculation and removal of excess surfactant (ethyl cellulose). e. Prepare an aqueous solution of NaCl in deionized water at a concentration of 0.04 g / ml. f. Add NaCl sol to the suspension while maintaining a 1:2 volume ratio between the suspension and the NaCl aqueous sol. g. Filter the aggregated graphene aerosol gel by vacuum filtration using a 0.45 μm pore size filter. h. Dry the solid powder overnight at 50 °C using a hot plate to obtain graphene-ethyl cellulose powder.

[0066] Step 4. Removal of larger graphene aerosol gel flakes. i. Redisperse the dry powder in ethyl alcohol solvent and filter through a 5 μm sieve. j. Re-agglomerating after steps (e), (f) and (g). Dry overnight using a 50°C hot plate.

[0067] Step 5. Preparation of the final graphene aerosol gel ink. 1. 60 mg of ethyl cellulose-graphene powder is slowly added to a mixture of 450 μL of cyclohexanone and 50 μL of terpineol. m. Using ultrasonic bath treatment at room temperature for 15 minutes, the powder is mixed in the solvent to obtain a homogeneous, suspended ink.

[0068] It was observed that when lower concentrations of ethyl cellulose were used in the ink formulation, the ink exhibited better conductivity after printing and thermal annealing.

[0069] Figure 7 shows a photograph of a supercapacitor device (interdigitated electrodes) approximately 1 cm x 1 cm printed with an aerosol-gel ink with a lower surfactant concentration. These devices were printed on polyimide (KAPTON) film using a 20 μm diameter printer tip using a single-pass printing method. After printing, the devices were annealed at 350 °C in nitrogen for 2 hours.

[0070] Nanoscale materials with tunable physical structures benefit uniquely from their large surface area exposure to the surrounding environment, which leads to numerous applications. However, significant bottlenecks, such as interparticle electrical resistance and mechanical breakdown, surface sensitivity to unwanted species, and the inability to control their defects, limit their potential for scalable and practical applications, such as renewable energy in the form of energy storage devices. Graphene has demonstrated significant physical properties over the past 15 years due to its atomic dimensions (thinness) and exceptional electronic properties due to its successful applications in energy and sensing. While the large-scale material synthesis aspect of graphene is in high demand, as opposed to micromechanical exfoliation methods, the fabrication of graphene devices and reliable exploration of their properties have yet to be adopted by industry. In one embodiment of the present invention, graphene aerosol gel is used to produce stable graphene aerosol gel inks by functionalizing surfactants and using them to fabricate printed graphene micro-supercapacitors on a number of substrate materials, including flexible and bendable substrates such as polyimide. It has been demonstrated that micro-supercapacitors with superior performance closely depend on the effective surface area of ​​the printed electrodes exposed to the electrolyte. As shown in more detail below, 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte and 5-10 μA cm -1 Over 10,000 operating cycles of discharge current density of 1000 kJ / s were obtained with the printed micro-supercapacitor electrochemical device with a capacitance retention of over 80%.

[0071] Ink characterization and printing The graphene aerosol-gel ink was characterized by a number of methods, including stability testing (qualitative observation of the settling of the suspension over time), aerosol-gel density estimation, electron microscopy, and post-printing electrical resistance measurements. For micro-supercapacitors, interdigitated electrodes were printed on polyimide substrates using a SonoPlot Microplotter II with a 20 μm nozzle size at room temperature. While multiple printing passes can be used to optimize supercapacitor properties, this study focuses on printed supercapacitor devices using a single pass, primarily due to the fabrication of microdevices for small power sources. Post-printing heat treatment was performed on the device at 350 °C for 2 h in an inert ambient environment of a 5% hydrogen-in-nitrogen mixture.

[0072] Graphene aerosol gels were synthesized by catalytically uninitiated electric spark-initiated detonation of an acetylene precursor (C2H2) with a controlled amount of oxygen in a 4 L chamber. The process during detonation can be summarized as the conversion of acetylene molecules to free carbon atoms or ions, followed by carbon aerosol formation, and a subsequent gelation process to form a gel called carbon aerosol gel (CAG). The detailed process of CAG, graphene aerosol gel, and their characterization have been previously reported, and several important parameters, such as the aerosol gel wall thickness, porosity, oxygen-to-carbon atom ratio, and carbon-carbon bonding characteristics (hybridization), have been investigated. The surface area of ​​the aerosol gel was tested using Brunauer-Emmett-Teller (BET) measurements before formulation into an aerosol gel ink.

[0073] Numerous characterizations, including Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy with local lattice spacing, and diffraction patterns from selected-area electron diffraction (SAED), confirmed the graphene properties of the ink components and ensured the quality of the aerosol-gel material. The suspension also maintained its particle dispersion without settling, ensuring ink quality for subsequent long-term use. The rheology and particle size of the ink are some of the most important parameters that determine not only the quality of the printed pattern, but also its physical and mechanical stability.

[0074] The micro-supercapacitor shown in Figure 7 is printed on a polyimide substrate, a 25 μm thick sheet that is mechanically very flexible and bendable, allowing for a high level of mechanical flexibility. In these devices, the cells are typically 10 mm x 8 mm and can be further miniaturized.

[0075] Figure 8 shows high-resolution transmission electron microscopy (HRTEM) imaging results for graphene aerosol-gel ink. The randomly distributed collapsed structure of the aerosol-gel particles (left image in Figure 8) indicates the graphene aerosol-gel signature. The image on the right (Figure 8) is a magnified view of the graphene aerosol-gel located in the area indicated by the circular region in the left image. The image shows the number of graphene layers present in typical aerosol-gel particles used in inks (7–10 parallel lines are visible from the TEM). It is important to understand that this unique structure, along with reliability in print quality (mechanical integrity), is an essential component for the development of energy storage devices.

[0076] To investigate the carbon-carbon bond characteristics of the printing device in more detail, Raman spectroscopy measurements were performed on the aerosol-gel ink. Figure 9 shows the vibrational spectrum of the aerosol-gel lattice shown in Figure 8 (the spot corresponding to the image shown in the insert is indicated as the measurement site). The G peak (approximately 1580 cm) -1 ) and 2D peak (approximately 2700 cm -1The appearance of the 2D peak indicates the presence of graphitic bonds in the structure. As shown in Figure 10 for the multilayer graphene lattice, the intensity of the 2D peak is expected to be smaller than that of the G peak due to the band structure (linear band structure with a Dirac point) that is different from that of single-layer graphene. -1 The D peak located nearby is assigned to a defect-derived peak, which is expected to occur in the Raman spectrum of the ink due to its quasi-3D random structure and the number of defects in the structure.

[0077] The printed micro-supercapacitors were tested for their electrochemical performance with a Gamry Instrument interface 1010E potentiostat / galvanostat device over a potential window of 0 V and 1 V. The electrolyte used in the cells was an ionic liquid electrolyte, namely, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4, an organic electrolyte). This is a room-temperature ionic liquid (IL) with a wide range of applications, including calibration of redox probes used to study electrochemical transport mechanisms, evaluation of single- or multi-electron redox processes, charge shuttling in electric double-layer capacitors (supercapacitors), and investigation of the reliability of electrode-electrolyte interfaces, to name a few.

[0078] Cyclic voltammetry analysis of the printed supercapacitor was performed at various scan rates (100 mV / s to 2,000 mV / s) between polarities of 0 V and 1 V applied to the two sets of finger electrodes. The rectangular current-voltage characteristics (particularly at lower scan rates, even at 1,000 mV / s) demonstrated the properties of electrochemical double-layer capacitance. Measurements were reliable over hundreds of cycles of operation at each of the lower scan rates, indicating the stability of the electrode-electrolyte interface. At higher scan rates (e.g., 2,000 mV / s), the current-voltage characteristics were somewhat distorted from the ideal rectangular shape, which requires further refinement.

[0079] The area-specific capacitance (CS ) can be measured from CV curves at different scan rates or from galvanostatic charge-discharge characteristics (discussed later). These are micro-supercapacitors, utilizing graphene aerosol gels with randomized structural signatures. Therefore, instead of deriving volumetric or gravimetric capacitances, it may be more appropriate to consider areal capacitances.

[0080] Figures 10a and 10b show the charge and discharge characteristics of the micro-supercapacitor using constant current measurements at 6 μA cm. -2 A constant current density of 1000 kJ / s was used.

[0081] The area-specific capacitance of a micro-supercapacitor is given by:

number

[0082] Figure 11 shows the expansion of material discovery into nanocarbon composites and their application to the fabrication of functional inks and energy devices (supercapacitors and battery devices) through additive manufacturing. Composites and inks include 1D nanotubes, 2D graphene, quasi-3D graphene aerosol gels, and carbon nanomaterials doped with elements such as nitrogen, sulfur, and boron.

[0083] [Example 4] Graphene aerosol gel ink formulation In this example, graphene aerosol gel ink was prepared and the physical characteristics and properties of interdigitated electrodes were tested.

[0084] Material Characterization The microstructure of graphene aerosol gel particles was examined using a Philips CM-100 transmission electron microscope at an accelerating voltage of 100 kV. TEM specimens were prepared directly on TEM copper grids by immersing the copper grids directly into the synthetic GAG ink. The surface morphology and uniformity of the printed electrodes were measured using a Hitachi field-emission scanning electron microscope (FESEM). Raman (Renishaw Invia Raman Microscope, excitation wavelength 532 nm) and XPS spectra (PHI 5000 Versa Probe II, Physical Electronics Inc.) were measured directly on the printed device to determine phase and elemental analysis. XPS spectra were achieved using a combination of electron and argon ion flood guns. The X-ray beam size was 100 μm, and survey spectra were recorded with a pass energy (PE) of 117 eV, a step size of 1 eV, and a dwell time of 20 ms, while high-energy resolution spectra were recorded with a PE of 23.5 eV, a step size of 0.05 eV, and a dwell time of 20 ms.

[0085] Aerosol Gel Ink Preparation The GAG ​​powder synthesized by the detonation method contained initial graphene nanosheet aggregates. Therefore, to disperse the aggregates, we used probe sonication for 30 minutes under ice-bath conditions using an ultrasonic probe (500 W, 20 kHz, Q500 sonicator, USA). 250 mg of GAG powder was dispersed in 50 ml of ethanol using 1 wt% ethyl cellulose (EC, Sigma-Aldrich, 5 wt%, 48% ethoxylated, 4 cP grade measured in 80:20 toluene:ethanol) as an emulsifier. The suspension was then filtered through a 5 μm glass fiber syringe filter to remove larger GAG particles. The collected suspension was then flocculated by adding an aqueous NaCl solution (0.04 g / ml in deionized water) followed by vacuum filtration using a 0.45 μm nylon filter. The resulting GAG / EC paste was then dried using a hot plate at 70 °C. The ink was prepared by homogeneously suspending the GAG / EC powder in cyclohexanone and terpinol (volume ratio 85:15) followed by ultrasonic bath treatment at a concentration of 70 mg / ml.

[0086] Inkjet printing of interdigitated electrodes (IDEs) Interdigitated electrodes (IDEs) of MSCs were patterned on flexible substrates using an inkjet printer (SonoPlot, Microplotter II, USA) with a glass tip and a 20 μm nozzle size at room temperature. The substrate was thoroughly cleaned by ultrasonic bath treatment in a mixture of acetone and methanol and dried by blowing with nitrogen gas before printing. The printed electrodes were then heat-treated at 350 °C for 2 h in a N2 / H2 mixture (5% hydrogen in nitrogen) to burn off the organic binder.

[0087] Electrochemical performance The electrochemical performance of the printed micro-supercapacitors was tested using a Gamry interface 1010E potentiostat / galvanostat in a potential window of 0 to 1 volt using 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF, Sigma Aldrich) organic electrolyte. Area-specific capacitance (C A ), volumetric capacity (C V ) and equivalent series resistance (R ESR ) is measured from the galvanostatic charge / discharge curves using equations (1), (2) and (3),

number

number

[0088] Results and Discussion Thermogravimetric analysis (TGA) was performed to measure the graphene content in the treated GAG / EC powder. TGA, showing the mass change as a function of temperature, indicated the decomposition of the surfactant at an onset temperature of approximately 250 °C. A significant change in mass (30 wt%) occurred between 250 °C and 350 °C, indicating the complete decomposition of the surfactant to aromatic compounds. Therefore, the GAG / EC powder contained 70 wt% graphene. The GAG / EC powder was further suspended in a cyclohexanone / terpinol mixture (volume ratio 85:15) to prepare inkjet printing ink.

[0089] The formulated inks demonstrated long-term stability and printability. Figures 12a and 12b show optical images of inkjet-printed interdigitated μ-SC and resistor elements, respectively, on flexible polyimide (25 μm thick) substrates. The geometric dimensions of the printed devices are listed in Table 1.

[0090] Table 1. Geometric measurements of inkjet-printed micro-supercapacitors [Table 1]

[0091] SEM and AFM images (SI-II) were recorded to determine the uniformity of the printed patterns. As can be seen from the SEM image in Figure 12c, the printed patterns are highly uniform and lack the coffee ring effect. Therefore, the ink flow was consistent and clump-free during the printing process, demonstrating good rheological properties of the formulated ink. The printability of the ink was investigated by printing multiple devices with twice the number of fingers. All printed patterns showed good uniformity. Furthermore, high-resolution images of the printed electrode surface were recorded by SEM to examine the surface morphology. See Figure 12d. The surface of the printed electrode contained spherical particles, forming a highly porous surface. Such a porous morphology is favorable for storage capacity.

[0092] Microstructural characterization The microstructure of GAG powder revealed by high-resolution TEM measurements is shown in Figure 13. Figure 13(a) shows aggregates of graphene nanosheets (GNSs) with a nearly uniform size distribution close to 100 nm. It is noteworthy that the edges of the GNSs have a more positive contrast than the center of the sheets, as shown in (b). As evident from the high-magnification image in (b), the boundaries of the GNSs essentially contain a shell-like structure, with the shell formed by edge-terminated graphene sheets, as shown in the inset image in (c). The randomly oriented sheets fuse to form a unique nanoporous system, i.e., an aerosol gel-like structure. The abundance of edge-terminated graphene resembles the morphology of a carbon onion, where graphene sheets are arranged concentrically to form a closed multishell structure, as shown in (d). In this case, the shell structure is limited only to the particle edges, and therefore the unique microstructure inherits porosity, which could benefit electrochemical energy storage.

[0093] Raman spectra of graphene aerosol gels Raman spectroscopy is used to characterize various sp 2 It can be used convincingly as a non-destructive, high-throughput characterization tool for carbon materials. The unique band structure of graphene resulted in the emergence of strong Raman bands due to resonant phonon scattering. Therefore, careful analysis of the Raman spectrum was used to reveal important microstructural aspects regarding defects, stacking order, number of layers, doping, stress, and thermal conductivity of graphene. The Raman spectrum of GAG particles recorded at room temperature was fitted with a Lorentzian function, revealing a band around 1351 cm. -1 , 1583cm -1 and 2700 cm -1 These optically Raman active phonon modes are typically assigned as the D, G, and 2D bands, respectively. 1g , E 2g and A 1g This is due to the overtones of the phonon mode. -1 and 2452 cm -1 Two weak Raman bands were also present.

[0094] These phonon modes were previously assigned as the D' and D+D'' bands, respectively. The origin of the D' band is due to the intravalley double resonance (DR) scattering process around the K (or K') point in the Brillouin zone. However, the D+D' mode is due to the 1100 cm -1 The strong 2D band is activated from a combination of the LA branch phonons and the D phonons at the K points of the Brillouin zone. The appearance of a strong 2D band is a signature of graphitic carbon. Furthermore, the line shape of the 2D band fits very well with a single Lorentzian function, similar to the 2D band of single-layer graphene (SLG). However, the wavenumber for the 2D band of SLG is about 20 cm. -1 The increase in and higher full width at half maximum (FWHM) was consistent with turbostatic stacking of graphene layers in GAG.

[0095] Furthermore, the intensity of the D band generally correlates with the defect density, which exists in the form of structural defects and irregular edges due to loss of translational symmetry. As seen from high-resolution TEM images, the microstructure of GAG contains a shell-like structure with an average size distribution of 100 nm. The shell boundaries are substantially bounded by edge-oriented graphene sheets that persist in the GAG ​​morphology. Therefore, intuitively, a large I(D) / I(G) ratio is expected for GAG due to the substantial amount of exposed edges, as previously shown for onion-like carbons. Conversely, a smaller I(D) / I(G) ratio of approximately 0.2 suggests not only a low concentration of structural defects but also edges where translational symmetry is well maintained. Thus, edges have either zigzag or armchair arrangements of carbon atoms, which results in a lower amount of edge defects. It has previously been shown that zigzag edges do not contribute effectively to the D band intensity due to momentum conservation, suggesting that the stripe-like structure contains a substantial density of edge-oriented graphene sheets with armchair arrangements of carbon atoms.

[0096] X-ray photoelectron spectroscopy The chemical purity of the GAG ​​was analyzed by XPS spectra recorded from the surface of the printed device. The survey spectrum showed only optical peaks associated with C1s carbon and very low oxygen concentrations. The asymmetric shape of the XPS band indicates a deconvolution into three components. The greater intensity of the XPS band is due to the sp carbon atoms, which originate from the C=C atoms in the hexagonal network of carbon atoms. 2 The sp hybridization state (284.05 eV) further confirmed the chemical purity of the GAG. 3 The hybrid state (284.7 eV) is also present in the XPS spectrum in significant concentration (22%) along with a minimum concentration of CO groups, which can be attributed to the size and abundance of graphene edge states that are chemically more active to react with oxygen.

[0097] Electrochemical performance The electrochemical performance of the printed GAG μ-SC, investigated by cyclic voltammograms (CV) at different scan rates, showed a potential window of 0.0–1.0 volts. The typical square shape of the CV curve indicated the ideal double-layer capacitance characteristics of the printed μ-SC. The square shape of the CV curve persisted linearly for the measured high scan rates up to approximately 2 V / s. However, the rounded corners suggested a significant amount of equivalent series resistance (ESR) present in the printed device. The ESR value was determined by the voltage drop at the start of the discharge curve (5 μ-amp / cm). 2 Calculated using equation (2) from ΔV = 36 mV at R ESR The magnitude of ESR was found to be about 45 kΩ. The magnitude of ESR arises from contact resistance, electrode-electrolyte interface resistance, and bulk electrode resistance. The high porosity of the GAG ​​electrode can be a major contributor to the magnitude of ESR. Furthermore, charge-discharge (CDC) profiles were measured on the MSCs at different current densities. The CDC exhibits a typical triangular shape profile, but asymmetric shapes are well known, especially at low current densities. However, at high current densities, the triangular shape becomes more symmetric. The area-specific capacitance (C A ) and volumetric capacity (C v) was calculated from the slope of the galvanostatic discharge profile using equations (2) and (3) as a function of current density. The stability of the printed supercapacitors was evaluated at 6 μ-amp / cm 2 The devices were tested for many CDC cycles at a constant current density of 10,000. The devices showed good capacity retention of about 80% after 10,000 cycles.

[0098] To increase power density for practical applications, multiple cells are typically assembled in series and parallel combinations, as shown in Figures 14a and 14b. The series combination showed a one-third decrease in capacity when operated in the 0-1 volt potential window, as expected, but showed a slight increase in charge / discharge time when operated up to 3 volts. Similarly, the parallel configuration showed a three-fold increase in capacity compared to a single cell. Therefore, the formulated GAG ink can be directly used to print multiple devices in series and parallel combinations to scale the power output.

[0099] conclusion All printed patterns showed high uniformity without any obvious smearing or coffee ring effect. Therefore, the good printability and long-term stability of the GAG ​​ink confirmed the success of the ink formulation protocol. The printed μ-SC showed a current of 6 μA cm in a potential window of 0–1 volt. -2 The graphene showed excellent capacity retention of about 80% over many charge-discharge cycles (10,000 cycles) operated at room temperature. Therefore, this approach could bridge the gap in mass production of graphene and fabrication of energy storage devices.

Claims

1. An ink composition comprising an amount of at least one nanomaterial selected from graphene, carbon nanotubes, and graphene aerosol gel.

2. The ink composition of claim 1 , wherein the quantity of at least one of graphene, carbon nanotubes, and graphene aerosol gel is dispersed in a liquid vehicle.

3. The ink composition of claim 2 , wherein the liquid vehicle comprises a mixture of one or more ketones and one or more alcohols.

4. The ink composition of claim 3 , wherein the liquid vehicle comprises cyclohexanone and terpineol.

5. 5. The ink composition of claim 4, wherein the liquid vehicle comprises from about 60% to about 99% by weight cyclohexanone and from about 1% to about 35% by weight terpineol.

6. The ink composition of claim 1, wherein the ink comprises from about 1 to about 500 mg / ml of a surfactant.

7. The ink composition of claim 1 , wherein the ink comprises from about 0.01 to about 10 mg / ml of the carbon nanotube and / or graphene aerosol gel.

8. The ink composition of claim 1 , wherein the composition further comprises an amount of graphene or graphene oxide particles.

9. The ink composition of claim 8, wherein the ink comprises from about 1 to about 30 mg / ml of the graphene or reduced graphene oxide particles.

10. 10. The ink composition of claim 1, wherein the graphene aerosol gel has a D90 particle size of about 0.1 to about 10 μm.

11. The ink composition of claim 1 , wherein the at least one nanomaterial is doped with at least one of nitrogen, sulfur, and boron.

12. An electronic device comprising one or more traces printed with the ink of any one of claims 1 to 11.

13. The electronic device of claim 12 , wherein the electronic device is a capacitor, a supercapacitor, a microcapacitor, an ultracapacitor, or a pseudocapacitor.

14. 1. A method of forming a composite ink, comprising: providing a graphene or graphene oxide-containing ink precursor comprising a quantity of graphene or graphene oxide particles dispersed in a liquid vehicle; dispersing a quantity of at least one of carbon nanotubes and graphene aerosol gel in the ink precursor; 10. A method of forming a composite ink, comprising:

15. providing the ink precursor, forming the liquid vehicle by combining at least one ketone and at least one alcohol; adding the amount of graphene or graphene oxide particles to the liquid vehicle; optionally adding a surfactant to the liquid vehicle and graphene or graphene oxide particle mixture; agitating the liquid vehicle and graphene or graphene oxide particle mixture, thereby dispersing the particles within the liquid vehicle; 15. The method of claim 14, comprising:

16. The method of claim 15 , wherein the agitating step comprises sonicating the ink precursor.

17. 16. The method of claim 15, wherein the ultrasonic treatment is carried out at a temperature of 400°C or less.

18. 15. The method of claim 14, wherein the step of dispersing the quantity of at least one of carbon nanotubes and graphene aerosol gel in the ink precursor comprises sonicating the ink precursor mixture.

19. 1. A method of forming an ink composition, comprising: providing a mixture comprising a graphene aerosol gel and a surfactant, preferably ethyl cellulose or nitrocellulose; dispersing the mixture in a liquid vehicle system, preferably comprising a mixture of one or more ketones and one or more alcohols, more preferably a mixture of cyclohexanone and terpineol; A method of forming an ink composition comprising:

20. A method of forming an electronic device comprising printing conductive traces onto a substrate using the composite ink of any one of claims 1 to 11.

21. The method of claim 20 , wherein the substrate comprises a flexible substrate formed from a synthetic resin material.

22. 22. The method of claim 21, wherein the synthetic resin material comprises a polyimide.

23. 21. The method of claim 20, wherein the method further comprises annealing the conductive traces.

24. 24. The method of claim 23, wherein the annealing step is carried out in an inert atmosphere at a temperature of about 200°C to about 500°C.

25. 25. The method of claim 24, wherein the annealing step is performed at a temperature of about 350°C under a nitrogen atmosphere.

26. 24. The method of claim 23, wherein the annealing step is carried out for a period of 1 to 5 hours.

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