WO2024146776A1

WO2024146776A1 - Flexible, biodegradable, metallized graphene fibre structure and process for production of the like

Info

Publication number: WO2024146776A1
Application number: PCT/EP2023/086590
Authority: WO
Inventors: Rakesh Nair; Hans KLEEMANN; Karl Leo
Original assignee: Technische Universität Dresden, Körperschaft des öffentlichen Rechts
Priority date: 2023-01-04
Filing date: 2023-12-19
Publication date: 2024-07-11

Abstract

In various embodiments, a process for producing a metallized graphene fibre structure is provided, said process comprising: providing a leaf structure from a plant leaf, where the provided leaf structure is a leaf skeleton; pretreating the leaf structure by means of a treatment medium to alter the electrical properties of the leaf structure in order to form a pretreated leaf structure; treating the pretreated leaf structure by means of a metal ion solution such that the leaf structure has a metallic coating; and heating the coated leaf structure in such a way that the leaf skeleton is converted to graphene, in order to form the metallized graphene fibre structure.

Description

Flexible, biodegradable, metallized graphene fiber structure and method for producing the same

Description

Various embodiments relate to a flexible, biodegradable, metallized graphene fiber structure and a method for making a flexible, biodegradable, metallized graphene fiber structure.

Graphene is considered the material of the future due to its optical transparency, very good electrical conductivity and chemical stability, for example in electronic devices as a practical replacement for indium tin oxide (ITO). The excellent mechanical strength of graphene may also offer the possibility of using it as a flexible electrode in portable electronic devices. In addition, with the increase in the amount of waste generated from electronic devices, it is desirable to make at least some of the components of electronic devices, such as the graphene fiber structures, recyclable.

US 2018/0083331 Al concerns a hybrid battery and capacitor system that uses carbon nanolayers in the electrodes.

Various embodiments relate to a method for producing a metallized graphene fiber structure, which can use simple techniques and inexpensive, biodegradable starting materials, and thus can be easily efficient, cost-effective and environmentally friendly.

Various embodiments relate to a flexible, biodegradable, metallized graphene fiber structure, which, in addition to its simple, efficient, cost-effective and environmentally friendly production, can have high light transmission and high electrical conductivity.

In various aspects, a method for producing a flexible, biodegradable, metallized graphene fiber structure may be provided, the method comprising: providing a leaf structure from a plant leaf, wherein the provided leaf structure is a leaf skeleton; pretreating the leaf structure using a treatment agent for changing the electrical properties of the leaf structure to form a pretreated leaf structure; treating the pretreated leaf structure using a metal ion solution such that the leaf structure may have a metallic coating (e.g., a continuous, closed metallic coating); heating the coated leaf structure such that the leaf skeleton may be converted to graphene to form the metallized graphene fiber structure.

By combining pretreatment and treatment of the sheet structure, the sheet structure can be converted into a graphene fiber structure by heating the pretreated, metal-coated sheet structure in a simple manner. For example, high-tech equipment (e.g. chemical vapor deposition, physical vapor deposition, vacuum chambers/inert atmosphere) or catalytic cost-intensive solutions may be unnecessary. In addition, the metal of the coating of the coated sheet structure can be sintered during heating. As a result, the resulting metallized graphene fiber structure can have a higher mechanical resistance. Furthermore, by using a naturally occurring quasi-fractal sheet structure, which is treated, modified and/or coated using a low-cost metal ion solution (e.g. without alternative, already known but costly metal particle filling techniques), an environmentally friendly, cost-effective method for producing a flexible, biodegradable, metallized graphene fiber structure can be provided. The process can make it possible to produce a flexible, printable, biodegradable, environmentally friendly, cost-effective graphene fiber structure, which can be used, for example, as a component for organic electronic devices.

According to various embodiments, the treating agent may comprise or consist of tridodecylmethylammonium chloride (TDMAC) or chitosan.

The treatment agent can enable a simple metal solution (e.g. also called metal ion solution), for example without nanoparticles and/or nanowires, to be used for metal coating the leaf structure (e.g. for treating the leaf structure). Furthermore, the treatment agent can improve the adhesion of the metal layer to the leaf veins of the leaf structure. This can enable metal coating (e.g. during treatment) of the thus pretreated leaf structure, for example by means of a simple immersion (e.g. by means of a dipping process or dip coating) without the need for further treatment of the leaf structure. Furthermore, the treatment agent can protect the fibers of the leaf structure from chemical and/or mechanical damage. For example, the treatment agent can protect against damage that can be caused by the solvents present in the metal ion solution.

TDMAC and chitosan have the advantage of being cost-effective. In addition, the electrical conductivity and transparency (e.g. light permeability or light transmission) of the resulting graphene fiber structure can be varied depending on the concentration of TDMAC or chitosan.

Chitosan has the additional advantage of being non-toxic and biodegradable, so that the entire manufacturing process can be based exclusively on biocompatible materials. Chitosan can also enable a better and more thorough coating of the fibers of the leaf structure, improved flexibility of the leaf structure without overloading the leaf skeleton, and improved hydrophilicity of the fibers of the leaf structure. which can ensure that the fibers of the leaf skeleton remain supple by locking in moisture.

According to various embodiments, the leaf structure can be coated with a polymer layer during the pretreatment, wherein the polymer layer can be formed by means of the treatment agent. The polymer layer can, for example, coat the leaf structure in such a way that the leaf veins of the leaf structure can be coated with the polymer layer in a conformal manner, e.g., completely surrounded.

The polymer layer, for example comprising or consisting of chitosan, can provide the leaf structure (e.g. each leaf vein of the leaf structure) with protection from ambient moisture and/or oxygen. This can enable the transformation of the leaf skeleton of the leaf structure to take place under conditions that do not require an inert atmosphere and/or vacuum.

According to various embodiments, the metal ion solution may comprise a metal, for example, wherein the metal may be silver.

Silver, for example, can have the advantage that the silver coating can retain good electrical conductivity even when oxidized under ambient conditions, eg to silver(I) oxide (Ag2O). This can be a better alternative than copper (Cu), which can be oxidized, for example, to copper oxide (CuO) or copper(I) oxide (C112O) under ambient conditions, whereby the corresponding electrical conductivity of copper oxide (CuO) or copper(I) oxide (Q12O) can be lower compared to silver(I) oxide ( _Ag2O ) (ie after oxidation).

According to various embodiments, treating the pretreated sheet structure may further comprise depositing a further metal layer comprising a further metal on the coated sheet structure to form a double-coated sheet structure. The further metal may be, for example, copper.

The further metal layer can be designed such that the light permeability (e.g. light transmission) of the resulting graphene fiber structure can be increased compared to the graphene fiber structure with a metal layer with a single metal, while at least as good electrical conductivity can be maintained. For example, the (first) metal layer can be designed as a seed layer for the further metal layer. For example, the (first) metal layer can have a thinner layer thickness in the double-coated sheet structure than in the sheet structure which is coated with a metal layer with a single metal.

According to a further aspect, a flexible, biodegradable graphene fiber structure can be provided. The graphene fiber structure can be used, for example, as a component for organic electronic components and/or devices. The graphene fiber structure can have a plant leaf graphene core structure. The plant leaf Graphene core structure can be coated with a metal layer (e.g. with a first metal layer), wherein the metal layer can be, for example, a silver layer.

Because the graphene fiber structure comprises or consists of naturally occurring, widely available raw materials (plant leaf structure), the graphene fiber structure can be produced cost-effectively and easily recycled and/or decomposed.

Furthermore, due to its flexible, interconnected structure (e.g., multiscale connections of leaf veins within the skeleton form a fractal-like (quasi-fractal) framework or skeleton), the plant leaf structure can provide increased mechanical and/or structural stability to the substrate.

Embodiments are shown in the figures and are explained in more detail below.

Show it

Figure 1 is a schematic flow diagram of a method for producing a flexible, biodegradable, metallized graphene fiber structure, according to various embodiments;

Figures 2A-C show views of a plant leaf during and after providing the leaf structure, according to various embodiments;

Figure 3 schematic side views of the step of treating the pretreated sheet structure, according to various embodiments; and

Figures 4A-C show views of leaf structures before and after metal coating, according to various embodiments; and

Figure 5 shows a hydroionic battery according to various embodiments.

In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "fore", "rear", etc. will be used with reference to the orientation of the figure(s) being described. Since components of embodiments may be positioned in a number of different orientations, the directional terminology is for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. It is to be understood that the features of the various exemplary embodiments described herein may be combined with one another unless specifically stated otherwise. The following description is therefore not to be taken in a limiting sense. and the scope of the present invention is defined by the appended claims.

In the context of this description, the term "leaf structure" (also called leaf skeleton or leaf framework) is understood, for example, to mean a plant leaf from which plant tissue (e.g. biomass) has been substantially completely removed such that only the skeleton or framework of the plant leaf, for example made of cellulose, lignin and/or hemicellulose, among others, which forms a coherent and/or cross-linked leaf vein structure, remains.

In the context of this description, the term "biodegradable" with regard to the substrate is understood to mean that it is a substrate which consists of components and/or materials, for example renewable raw materials, the majority of which, for example more than 80%, for example more than 90% of which, can dissolve or decompose into its elementary components such as carbon, oxygen, hydrogen, carbon dioxide, humic acids, etc. . . and/or other minerals under the influence of external factors (enzymes, (micro)organisms, electromagnetic radiation (e.g. UV and light radiation), pressure, solvents (e.g. water), etc. . . ) within a certain period of time (for example a period of time which is longer than the usual periods of the manufacturing process of the substrate and/or the organic electronic components, for example 10, 20, 50 times longer).

The term "metal ions" in relation to the solution for coating the sheet structure is used in this description to mean a solution in which the metal is essentially dissolved in the solution or partially in suspension (e.g. in which the metal is essentially dissolved in the solution and optionally partially in suspension). Solutions comprising metal nanoparticles or metal nanowires, for example in suspension in the solution, are not a metal ion solution in the sense of this invention.

The term “flexible” with regard to the graphene fiber structure is used in this description to mean that the graphene fiber structure is bendable, flexible, elastic, mobile and/or articulated in several folding directions up to small bending radii without damage.

In the context of this description, the term "graphene fiber structure" is used to refer to a structure which at least partially comprises graphene and/or graphite, for example graphene and optionally graphite. The graphene fiber structure described here can be used as such in a fully functional manner, for example as an electrically conductive component for electronic devices. For example, the graphene fiber structure described here can be a core structure, for example called a plant leaf graphene core structure, which at least partially comprises graphene and/or graphite (for example graphene and optionally graphite); a core structure deposited polymer layer; and at least one metal layer deposited on the polymer layer.

In the context of this description, the term "plant leaf graphene core structure" is understood to mean the plant leaf structure (also called plant leaf framework or skeleton), e.g. made of cellulose, lignin and/or hemicellulose, which is at least partially converted into graphene and/or graphite (e.g. graphene and optionally graphite) by means of energy input (e.g. heat). The plant leaf graphene core structure described here is, for example, part of the graphene fiber structure (e.g. the core of the graphene fiber structure).

Figure 1 illustrates a schematic flow diagram of a method for producing a flexible, biodegradable graphene fiber structure, according to various embodiments.

According to various embodiments, the method 1 for producing a flexible, biodegradable, metallized graphene fiber structure can comprise providing 100 a leaf structure 10 from a plant leaf. The leaf structure provided can be a leaf skeleton. The method 1 can further comprise pretreating 200 the leaf structure 10 by means of a treatment agent for changing the electrical properties of the leaf structure 10 in order to form a pretreated leaf structure 20. In addition, the method 1 can comprise treating 300 the pretreated leaf structure 20 by means of a metal ion solution 30 such that the leaf structure 24 can have a metallic coating (e.g. a continuously closed metallic coating). Furthermore, the method 1 can, for example, comprise heating 400 the coated leaf structure 24 in such a way that the leaf skeleton can be converted to graphene in order to form the metallized graphene fiber structure.

By combining pretreatment and treating the sheet structure, converting the sheet structure into a graphene fiber structure by heating the pretreated, metal-coated sheet structure can be done in a simple manner, for example without high-tech equipment (e.g. chemical vapor deposition, physical vapor deposition, vacuum chambers/inert atmosphere) or without catalytic cost-intensive solutions. Furthermore, by using a naturally occurring quasi-fractal sheet structure which is treated, modified and/or coated using a low-cost metal ion solution (e.g. without alternative, already known but costly metal particle filling techniques), an environmentally friendly, cost-effective method for producing a flexible, biodegradable, metallized graphene fiber structure can be provided. The process can make it possible to produce a flexible, printable, biodegradable, environmentally friendly, cost-effective graphene fiber structure, which can be used, for example, as a component for organic electronic devices.

Method 1 is described in detail using Figures 2 and 3. Figures 2A-C illustrate views of a plant leaf during and after providing the leaf structure, according to various embodiments.

According to various embodiments, providing 100 a leaf structure 10 may comprise providing 102 a plant leaf, the plant leaf comprising leaf veins and a plant tissue (e.g., biomass) disposed between and/or around the leaf veins; treating 104 the plant leaf such that the plant tissue can be removed from the plant leaf; and drying 106 the treated plant leaf to form the leaf structure 10.

According to various embodiments, the leaf structure 10 can be a plant leaf skeleton or a plant leaf framework. For example, the leaf structure can be made from a plant leaf that may have been degreened. In the leaf structure 10, for example, essentially only the leaf veins can remain from the plant leaf (e.g. without plant tissue). According to various embodiments, the leaf veins can, for example, essentially retain their three-dimensional, for example network-like and/or quasi-fractal structure that they had in the plant leaf before treatment.

According to various embodiments, the plant leaf can, for example, come from local plants. For example, the plant leaf can come from magnolia tree, rubber tree (e.g. Hevea brasiHensis), Bodhi tree (e.g. Ficus reHgiosa), Rooibos (e.g. Fagus sylvatica) or from plants with large leaves (e.g. lotus, rhubarb, banana trees, etc.). The plant leaf can be washed before treatment, for example by means of a solvent, for example an alcoholic solvent.

According to various embodiments, treating 104 the plant leaf may comprise immersing the plant leaf in an alkaline medium, for example together with heating the plant leaf immersed in the alkaline medium (for example at a temperature in a range of 60°C to 100°C) to form the leaf structure.

Example of providing 100 the leaf structure 10

Magnolia leaves were freshly obtained from local plants and washed under running water before being placed in an ultrasonic bath with ethanol for 10 minutes to remove contaminants. The leaves were then cut to a size of 2.5 x 2.5 cm and subsequently the samples were placed in an aqueous solution of Na2CO3.10 H2O (sodium carbonate decahydrate/washing soda) in demineralized water and heated overnight at a constant temperature of 90°C with stirring. The amount of Na2CO3.10 H2O to be used was determined by simply increasing the amount until the compound no longer dissolved. The samples were then removed and placed in a separate vessel containing fresh distilled water at room temperature, which was then placed in an ultrasonic bath for 20 minutes. The entire process was repeated until the water no longer changed color after the bath. The leaf veins were clearly visible at this point (see Figure 2A, which shows a magnolia leaf during the alkaline process) and a light brushing with gloved fingers was sufficient to remove excess biomass. The leaf skeletons were then bleached in a 10% bleach solution for 15 minutes before being dried and smoothed with weights.

Figure 2B shows the magnolia leaf after alkaline treatment. Figure 2C shows the treated magnolia leaf under magnification (scale bar - 500 pm).

According to various embodiments, the leaf structure 10 provided can be subjected to a pretreatment 200 using a treatment agent before being coated with a metal layer. The treatment agent can modify or change the electrical properties of the leaf structure 10. For example, the treatment agent can charge the fibers (e.g. the surface) of the leaf veins of the leaf structure 10 with at least partially positive charges.

By changing the electrical properties of the leaf structure, the treatment agent can enable a normal metal solution (e.g. metal ion solution), for example without nanoparticles and/or nanowires, to be used in the step of metal coating (e.g. treating) the leaf structure. Furthermore, the treatment agent can improve the adhesion of the metal layer to the leaf vein. This makes it possible to metal coat the leaf structure thus pretreated, for example by means of a simple dipping (e.g. by means of a dipping process or dip coating) without any further (pre)treatment of the leaf structure. Furthermore, the treatment agent can protect the fibers of the leaf structure, for example, from chemical and/or mechanical damage. For example, the treatment agent can protect against damage that can be caused by the solvents present in the metal ion solution.

According to various embodiments, the treatment agent can comprise or consist of an ion attractor and/or a cationic polymer. As a result, the treatment agent can modify the leaf structure in such a way that the pretreated leaf structure can electrostatically attract the metal ions (e.g. the metal particles from the metal ion solution) in order to attach the metal ions to the leaf veins of the leaf structure.

Tridodecylmethylammonium chloride (TDMAC) or chitosan can enable metal coating using a cost-effective metal ion solution. Thus, it can be used for the Metal coating avoids the use of costly metal particle filling techniques, for example comprising nanoparticles or nanowires, as may be the case with conventional ammonium bromide solutions.

TDMAC and chitosan have the advantage of being cost-effective, for example compared to conventional treatment agents such as PdCh. In addition, the electrical conductivity and transparency (e.g. light transmittance) of the resulting graphene fiber structure can be varied, adjusted and/or controlled depending on the concentration of TDMAC or chitosan during pretreatment.

TDMAC contains a positive charge. Pretreating the leaf structure with TDMAC can result in at least a partial positive charge along the fibers of the leaf veins of the leaf structure to attach the metal ions, for example, to the leaf veins of the leaf structure.

Chitosan is a naturally occurring (bio)polymer with cationic properties to which metal particles can be attached. Chitosan has the advantage of being biocompatible, non-toxic and biodegradable, so that the entire manufacturing process can be based exclusively on biocompatible materials. Chitosan can also enable a better and more thorough coating of the fibers of the leaf structure, improved flexibility of the leaf structure without overloading the leaf skeleton, and improved hydrophilicity of the fibers of the leaf structure, which can ensure that the fibers of the leaf skeleton remain supple by being able to lock in moisture.

According to various embodiments, the pretreatment 200 of the leaf structure can comprise immersing the leaf structure in a solution which comprises or consists of the treatment agent. The treatment agent can be present in the solution, for example, in a concentration in a range from 5 mM to 20 mM, for example 10 mM. According to various embodiments, the immersion can be carried out, for example, at a temperature which can be in a range from 25 °C to 120 °C, for example from 40 °C to 100 °C, for example 90 °C. According to various embodiments, the immersion can be carried out, for example, for a certain period of time in a range from 1 minute to 10 minutes, for example 5 minutes.

According to various embodiments, the pretreated leaf structure can be dried, for example by hanging the pretreated leaf structure on a hot air hanger or on hooks to dry, for example at room temperature.

According to various embodiments, the pretreatment 200 of the leaf structure, for example with chitosan, can be carried out in such a way that the leaf structure can be coated with a polymer layer (for example with a chitosan polymer layer). The polymer layer can, for example, have an average layer thickness in a range from 0.2 pm to 200 pm, wherein the polymer layer can, for example, serve as a seed layer for different metals (eg silver) can be used. The average layer thickness can be varied, for example, according to the viscosity and surface tension of the polymer solution (eg the chitosan solution).

Example of pretreatment 200 of the leaf structure 10

The pretreatment of the leaf structure is done by soaking it in a 10 mM solution of tri-dodecylmethylammonium chloride (TDMAC) or chitosan at 90 °C for 5 minutes. The increased temperature can thermally expand the pores of the leaf structure, thus allowing thorough penetration of the TDMAC or chitosan molecules from the solution.

Figure 3 illustrates schematic side views of the step of treating the pretreated sheet structure of the method for producing a flexible, biodegradable, metallized graphene fiber structure, according to various embodiments.

According to various embodiments, the treatment 300 of the pretreated leaf structure 20 can be carried out in such a way that at least some leaf veins of the leaf structure 20, for example each leaf vein of the leaf structure 20, can be coated with the metal layer in a conformal manner, e.g. completely surrounded. The coating of the leaf veins of the pretreated leaf structure 20 with the at least one metal layer can enable the electrical conductivity of the pretreated leaf structure 20 to be increased.

According to various embodiments, the treatment 300 of the pretreated sheet structure 20 may include an oblique introduction 302 of the pretreated sheet structure 20 into the metal solution 30. For example, the pretreated sheet structure 20 may be introduced into the metal solution 30 at an angle > relative to the surface of the metal solution 30 (e.g. from the horizontal plane) in a range of 10° to 60°. The oblique introduction 302 of the pretreated sheet structure 20 into the metal solution 30 may, for example, minimize or prevent bulging of the pretreated sheet structure 20, and thus bulging of the resulting graphene fiber structure.

According to various embodiments, the treatment 300 of the pretreated sheet structure 20 may further comprise immersion 304 of the sheet structure 20 in the metal solution 30, for example such that the sheet structure 20 can be completely immersed in the metal solution 30. The immersion 304 may be carried out for a certain period of time from 30 seconds to 2 minutes, and/or for example at a temperature in a range from 20°C to 60°C, for example at room temperature. In the case that chitosan is used as the polymer, the coating may This can be based, for example, on the chemical adhesion of metal ions to the amine groups in chitosan. This means that the process can be carried out at room temperature. The chemical adhesion of metal ions can also work when the temperature is increased, so that no energy needs to be used to increase the temperature.

According to various embodiments, the metal ion solution 30 may comprise or consist of a metal. The metal may be silver, for example.

Silver, for example, can have the advantage that the silver coating can retain good electrical conductivity even when oxidized under ambient conditions, e.g. in silver(I) oxide (Ag2O). This can be a better alternative than copper (Cu), which can be oxidized under ambient conditions, e.g. in copper oxide (CuO) or copper(I) oxide (CO), whereby the corresponding electrical conductivity of copper oxide (CuO) or copper(I) oxide (Q12O) can be lower than that of silver(I) oxide ( _Ag2O ).

According to various embodiments, the metal ion solution 30 may have a viscosity that may be in a range of 1xlO' ³ Pa- s to 50 Pa s.

According to various embodiments, the method may further comprise, for example, removing 306 (e.g., removing or pulling out) the leaf structure 20 from the metal solution 30. The removing 306 of the leaf structure 20 from the metal solution 30 may, for example, be performed such that a conformal (e.g., uniform) coating of the leaf structure 20 with a metal layer from the metal solution 30 near the Landau-Levich regime can be achieved to form the treated leaf structure 24.

For example, as shown in Fig.3, the Landau-Levich regime may start from a static meniscus 32 near the surface of the metal solution bath 30, with the dynamic meniscus 34 located directly above the static meniscus 32, in which the liquid may be sheared upwards, resulting in a uniformly thick metal layer 22 on the sheet structure.

According to various embodiments, this layer thickness (h) at low pulling speeds (~ 1 mm/s) can be approximately calculated as follows:

»-"JcV) ⁽¹⁾ where h is the layer thickness, > is the liquid viscosity, V is the constant pulling rate and > D is the surface tension.

However, since the Landau-Levich equation (1) is well applicable to Newtonian fluids and the ethyl cellulose polymer solution can behave rather in the non-Newtonian shear thinning regime, due to the complex and nonlinear rheological Properties of non-Newtonian fluids several approximations can be selected from the literature.

An extension of the Landau-Levi ch analysis by Gutfinger and Tallmadge “Film of nonnewtonian fluids adhering to flat plates”, AIChE Journal, vol. 11, no. 3, p. 403-413, 1965 takes into account the shear thinning of non-Newtonian fluids, where the layer thickness can be given by equation (2): where h is the layer thickness, k is the viscosity of the non-Newtonian fluid, V is the constant pulling velocity, > is the surface tension, > is the fluid density and g is the acceleration due to gravity. For a Newtonian fluid, the viscosity would not be a complex variant, so equation (2) returns to the Landau-Levich regime for n = 1 and k = >.

According to various embodiments, the treating 300 of the sheet structure 20 may further include a step of drying 308 of the treated sheet structure 24, for example to remove the excess metal from the sheet structure 22. The drying 308 may be carried out, for example, at room temperature.

According to various embodiments, the method may comprise a step of curing the treated sheet structure, for example at a temperature in a range of 70 °C to 120 °C, for example 90 °C and/or for a certain period of time in a range of 5 minutes to 30 minutes, for example 15 minutes.

According to various embodiments, the method 1 further comprises adjusting a predefined electrical conductivity of the metal layer and/or the resulting graphene fiber structure by adjusting a chemical concentration of the treatment agent during the pretreatment 200 of the sheet structure 10.

According to various embodiments, the method may further comprise heating the metal-coated sheet structure such that the sheet skeleton can be converted to graphene to form the metallized graphene fiber structure. The heating may, for example, be carried out at a temperature in a range of 500°C to 900°C. For example, the temperature of the heating may be chosen such that the metal of the metal coating can be sintered during heating. As a result, the resulting metallized graphene fiber structure may have a higher mechanical resistance. Alternatively or additionally, the heating may, for example, be carried out under ambient pressure and/or under ambient air, for example due to the multiple coatings of polymers/different metals on the sheet fibers, which can form a good moisture and oxygen barrier. Thus, for example, the need for a vacuum/inert environment during heating can be reduced. According to various embodiments, a flexible, biodegradable, metallized graphene fiber structure 24 can thus be provided by means of the method described herein, for example as a component for organic electronic components, wherein the graphene fiber structure 24 can have a plant leaf graphene core structure which can be coated with a metal layer (eg with a first metal layer). For example, the (first) metal layer can be a silver layer.

According to various embodiments, the plant leaf graphene core structure can have a plurality of leaf veins, wherein the leaf veins of the plant leaf graphene core structure can be coated conformally with the metal layer. The coating of the plant leaf graphene core structure can be designed such that the metal layer can form a closed layer (e.g. a continuously closed layer) over or on the plant leaf graphene core structure. According to various embodiments, the metal layer can be designed such that holes, gaps, and/or openings can be formed between at least some of the leaf veins. Alternatively or additionally, the metal layer can be designed such that the metal layer can connect at least two adjacent leaf veins of the plant leaf graphene core structure to one another.

According to various embodiments, the metal layer of the plant leaf graphene core structure may have an average layer thickness (e.g. around the leaf veins) which may be in a range of 100 nm to 500 pm.

According to various embodiments, the graphene fiber structure can have a polymer layer between the plant leaf graphene core structure and the metal layer. The polymer layer can comprise chitosan or consist thereof, for example when the pretreatment is carried out with chitosan. According to various embodiments, the chitosan polymer layer can have an average layer thickness in a range from 0.2 pm to 200 pm.

According to various embodiments, the graphene fiber structure produced by the method described here can have a surface resistance which can be in a range from 0.05 Q to 0.6 Q. Alternatively or additionally, the graphene fiber structure produced here can The graphene fiber structure described can have a light transmission that can range from 60% to 80%.

Example of treating 300 the pretreated leaf structure 20

The 2.5 cm ² pretreated leaf structures were dipped in silver screen printing ink that had been adjusted to a suitable viscosity in the laboratory (in this case a viscosity of 5 to 10 Pa s). Immediately after coating, the leaf structures treated in this way were clamped between laboratory tissues and pressure was applied to remove the silver screen printing ink that did not adhere to the fibers of the leaf structure. The leaf structures were then cured at 90 °C for 15 minutes.

Figures 4A-C illustrate top views of pretreated leaf structures before and after metal coating, according to various embodiments. In detail, Figure 4A shows the provided leaf structure after pretreatment 200 and before treatment 300 (200 pm scale bar). On Figures 4B (500 pm scale bar) and 4C (200 pm scale bar) a pretreated, silver-coated leaf structure is shown.

According to various embodiments, the heating step may be performed, for example, as described in M. Dudynski et al., GRAPHENE STRUCTURES IN CHARCOAL, Conference: Venice 2016 Sixth International Symposium on Energy from Biomass and Waste at: Great School of St. John the Evangelist, Venice, Italy, November 2016.

Example of heating 400 of the coated sheet structure 24

The process of heating can be carried out in a vacuum crucible, for example. The chamber is purged of oxygen after the sample is placed in it and kept at a pressure of at least -800 mBar. After a certain time, during which the sample is allowed to outgas, the chamber is filled with either a gas of choice to create an inert atmosphere (e.g. nitrogen, argon, etc.) or with a gas that promotes graphene/char formation (e.g. methane, etc.). After that, the temperature is continuously increased up to at least 800-950 °C, releasing the water and gases trapped in the lignocellulose cell matrix through tiny imperfections in the metal coating, transforming the biomass into activated carbon with graphene microstructures.

Figure 5 illustrates a hydroionic battery according to various embodiments.

According to various embodiments, the graphene fiber structure can have additional functions due to its electrically conductive property. For example, the graphene fiber structure can be used in a hydroionic battery 500. As shown in Figure 5, the graphene fiber structure 520 can be used in the hydroionic battery 500 as an electrically conductive, hygroscopic material between two electrodes (e.g. made of copper). Due to its porous structure, the graphene fiber structure 520 in the hydroionic battery 500 can absorb an aqueous salt solution 530 (e.g. electrolyte) by capillary action, for example, from a first electrode 540 to a second electrode 510 when the graphene fiber structure 520 is in contact with the aqueous salt solution 530. According to various embodiments, the treatment agent (e.g. TDMAC or chitosan) trapped in the graphene fiber structure 520 and/or the polymer layer (e.g. comprising TDMAC or chitosan) can be positively charged so that the graphene fiber structure 520 can attract electrons from the aqueous salt solution 530. According to various embodiments, the metal layer of the graphene fiber structure 520 can enable the movement of electrons from the first electrode 540 to the second electrode 510. According to various embodiments, the aqueous salt solution taken up (e.g. absorbed) by the hygroscopic material of the graphene structure can leave the hygroscopic material by evaporation 550. During evaporation, an energy gradient can arise which can draw more electrolyte into the battery through the capillary effect. The electrons from the aqueous salt solution can thus continue to circulate from the first electrode to the second electrode. This allows new electrons to be supplied to the battery, which can continue to supply current. According to various embodiments, the hydroionic battery 500 can generate an electrical voltage of 200 mV to 500 mV, for example 200 mV, and current of 350 pA to 500 pA, for example 350 pA.

According to various embodiments, pretreatment with a treatment agent can result in better adhesion of metal (and thus better electrical conductivity). The better metal adhesion can close many of the pores of the fibers of the sheet structure and reduce the light transmittance. According to various embodiments, the light transmittance can be increased while the high electrical conductivity and/or the low sheet resistance are not impaired, for example by means of a double coating of the sheet structure with different metals.

For this purpose, the graphene fiber structure can be formed, for example, by means of the method described above, wherein the (e.g. first) metal layer can be a thinner layer thickness than in the embodiments in which the graphene fiber structure has a metal coating with a single metal.

According to various embodiments, in order to form a thinner (e.g. first) metal layer, the metal ion solution 30 may have a viscosity which may, for example, be in a range of 5 Pa s to 10 Pa s.

According to various embodiments, treating 300 the pretreated sheet structure 20 (prior to heating 400) may further comprise depositing 310 another (eg, second) metal layer comprising another (eg, second) metal on the coated sheet structure 24 to form a double-coated sheet structure. The Deposition 310 may include, for example, electroplating and/or atomic layer deposition. According to various embodiments, deposition 310 may be performed using a direct current in a range of 10 mA to 100 mA.

Thus, a graphene fiber structure can be provided which can be coated with a first metal layer and a second metal layer arranged on the first metal layer. The first metal layer can serve, for example, as a seed layer for the second metal layer. According to various embodiments, the first metal layer can comprise or consist of a first metal, and the second metal layer can comprise or consist of a second metal. According to various embodiments, the first metal and the second metal can be different from one another. For example, the first metal can be silver, and the second metal can be copper.

According to various embodiments, the first metal layer can, for example, have an average layer thickness that can be in a range from 100 nm to 100 pm. Alternatively or additionally, the second metal layer can, for example, have an average layer thickness that can be in a range from 100 nm to 10 pm.

According to various embodiments, electroplating may, for example, be carried out until a certain (e.g. desired) electrical conductivity can be achieved.

Example of coating the leaf structure with a first metal layer and a second metal layer

A silver layer was applied to the 2.5 cm ² TDMAC-treated sheet structure by immersing the provided sheet structure in silver solution (e.g. silver ink) with a viscosity of less than 10 Pa s (e.g. a viscosity value close to that of inkjet printing inks) and/or with a concentration of 5% to 30%. This resulted in the layer thickness of the silver layer being thinner than in the example given above. The sheet resistance of the silver-coated sheet structure was 72 Q instead of the previous values of less than 0.5 Q (clearly indicating a reduced (e.g. thinner) silver layer). This layer was used as a seed layer for the deposition of atomic copper (Cu) by electroplating using a solution of CuSOvFFO (generic copper salt) at a concentration of 0.15 M dissolved in water at a direct current of 20 mA to 200 mA DC.

According to various embodiments, method 1 may further comprise adjusting a predefined electrical conductivity of the graphene fiber structure by adjusting the current applied during electroplating. According to various embodiments, after the heating step, for example, which can be carried out as described above, the resulting double-coated graphene fiber structure can have a surface resistance which can be in a range from 1 Ω to 500 Ω. Alternatively or additionally, the graphene fiber structure described here can have a light transmission which can be in a range from 60% to 90%. Alternatively or additionally, the graphene fiber structure described here can have an electrical conductivity which can be in a range from 1 S/m to ¹⁰⁰ S/m.

According to various embodiments, during heating, the first metal of the first metal layer and the second metal of the second metal layer may, for example, be sintered. In that case, the average layer thickness of the first metal layer may be different than before heating. Alternatively or additionally, the average layer thickness of the second metal layer may be different than before heating.

According to various embodiments, the first metal layer can, for example, have an average layer thickness that can be in a range from 500 nm to 100 pm. Alternatively or additionally, the second metal layer can, for example, have an average layer thickness that can be in a range from 100 nm to 10 pm.

The following describes some examples that relate to what is described herein and shown in the figures.

Example 1 is a method for producing a flexible, biodegradable, metallized graphene fiber structure, comprising: providing a leaf structure from a plant leaf, wherein the provided leaf structure is a leaf skeleton; pretreating the leaf structure using a treatment agent for changing the electrical properties of the leaf structure to form a pretreated leaf structure; treating the pretreated leaf structure using a metal ion solution such that the leaf structure has a metallic coating (e.g., a continuous, closed metallic coating) (preferably so that a coated leaf structure is formed which has the metallic coating and the pretreated leaf structure coated therewith).

In Example 2, the method according to Example 1 can further optionally be arranged such that the treating agent comprises tridodecylmethylammonium chloride or chitosan.

In Example 3, the method according to Example 1 or 2 may further optionally be arranged such that the sheet structure is coated with a polymer layer during the pretreatment, wherein the polymer layer is formed by means of the treatment agent. In Example 4, the method according to Examples 1 to 3 can be further optionally configured such that treating the pretreated sheet structure comprises immersing the pretreated sheet structure in the metal ion solution for metal coating the pretreated sheet structure to form the coated sheet structure.

In Example 5, the method according to Examples 1 to 4 can further optionally be arranged such that the heating takes place at a temperature in a range from 500 ° C to 900 ° C, for example under ambient pressure and/or under ambient air.

In Example 6, the method according to Examples 1 to 5 may further optionally be arranged such that the metal ion solution comprises a metal which is silver.

In Example 7, the method according to Examples 1 to 6 can further optionally be arranged such that the metal ion solution has a viscosity which is in a range from 5 Pa-s to 50 Pa-s.

In Example 8, the method according to Examples 1 to 6 can further optionally be arranged such that the metal layer of the coated sheet structure has an average layer thickness which is in a range of 500 nm to 100 pm.

In Example 9, the method according to Examples 1 to 6 may further optionally be configured such that treating the pretreated sheet structure further comprises depositing a further metal layer comprising a further metal on the coated sheet structure to form a double-coated sheet structure, for example wherein the further metal is copper.

In Example 10, the method according to Example 9 in combination with any of Examples 1 to 6 may further optionally be configured such that the double-coated sheet structure comprises a first metal layer formed by means of the metal ion solution and a second metal layer formed on the first metal layer.

In example 11, the method according to example 9 or 10 can further optionally be configured such that the (e.g. first) metal layer (e.g. a first metal layer of the metal layer) has (or consists of) a first layer thickness which is in a range from 200 nm to 350 pm, and/or wherein the second metal layer has a second layer thickness which is in a range from 100 nm to 10 pm.

Example 12 is a flexible, biodegradable, metallized graphene fiber structure, wherein the graphene fiber structure comprises a plant leaf graphene core structure coated with a first metal layer, for example wherein the first metal layer is a silver layer. In Example 13, the graphene fiber structure according to Example 12 may further optionally be configured such that the graphene fiber structure comprises a second metal layer on the first metal layer, for example wherein the second metal layer is a copper layer.

In Example 14, the graphene fiber structure according to Example 13 can be configured such that the first metal layer has a first layer thickness which is in a range from 500 nm to 100 pm, and/or wherein the second metal layer has a second layer thickness which is in a range from 100 nm to 10 pm.

In Example 15, the graphene fiber structure according to any one of Examples 12 to 14 may be configured such that the graphene fiber structure comprises a polymer layer between the plant leaf graphene core structure and the first metal layer, for example wherein the polymer layer comprises chitosan.

Example 16 is configured according to any one of Examples 1 to 15, wherein the metal ion solution comprises or consists of a solution comprising metal ions, e.g. comprising dissolved metal (wherein the e.g. metal is substantially dissolved in the solution and optionally partially in suspension).

Example 17 is configured according to any one of Examples 1 to 16, wherein the metal ion solution: is free of metal particles (e.g., nanoparticles and/or nanowires), or at least comprises more (e.g., dissolved) metal that preferably provides the metal ions than metal that provides metal particles (e.g., nanoparticles and/or nanowires) and/or is in suspension.

Claims

Patent claims

1. A method (1) for producing a flexible, biodegradable, metallized graphene fiber structure, comprising

- providing (100) a leaf structure (10) from a plant leaf, wherein the provided leaf structure is a leaf skeleton;

- pretreating (200) the sheet structure by means of a treatment agent for changing the electrical properties of the sheet structure (10) to form a pretreated sheet structure (20);

- treating (300) the pretreated leaf structure (20) by means of a metal ion solution (30) such that the leaf structure (24) has a metallic coating;

- Heating (400) the coated sheet structure (24) such that the sheet skeleton is converted to graphene to form the metallized graphene fiber structure.

2. The method (1) according to claim 1, wherein the treating agent comprises tridodecylmethylammonium chloride or chitosan.

3. Method (1) according to claim 1 of 2, wherein the sheet structure (10) is coated with a polymer layer during the pretreatment (200), the polymer layer being formed by means of the treatment agent.

4. The method (1) of any one of claims 1 to 3, wherein treating (300) the pretreated sheet structure (20) comprises immersing (304) the pretreated sheet structure (20) in the metal ion solution (30) for metal coating the pretreated sheet structure (20) to form the coated sheet structure (24).

5. Method (1) according to one of claims 1 to 4, wherein the heating (400) takes place at a temperature in a range of 500 °C to 900 °C, preferably under ambient pressure and/or under ambient air.

6. The method (1) according to any one of claims 1 to 5, wherein the metal ion solution (30) comprises a metal which is silver.

7. Method (1) according to one of claims 1 to 6, wherein the metal ion solution (30) has a viscosity which is in a range from 5 Pa s to 50 Pa s.

8. Method (1) according to one of claims 1 to 7, wherein the metal layer of the coated sheet structure (24) is a continuously closed metal layer, and/or wherein the metal layer of the coated sheet structure (24) has an average layer thickness which is in a range from 500 nm to 100 pm.

9. The method (1) of any of claims 1 to 6, wherein treating (300) the pretreated sheet structure (20) further comprises depositing (310) a further metal layer comprising a further metal on the coated sheet structure (24) to form a double-coated sheet structure, preferably wherein the further metal is copper.

10. The method (1) according to claim 9 in combination with any one of claims 1 to 6, wherein the double-coated sheet structure comprises a first metal layer formed by means of the metal ion solution (30) and a second metal layer formed on the first metal layer.

11. Method (1) according to claim 10, wherein the first metal layer has a first layer thickness which is in a range from 500 nm to 100 pm, and/or wherein the second metal layer has a second layer thickness which is in a range from 100 nm to 10 pm.

12. A flexible, biodegradable, metallized graphene fiber structure, wherein the graphene fiber structure comprises a plant leaf graphene core structure coated with a metal layer.

13. Graphene fiber structure according to claim 12, wherein the first metal layer comprises silver, and/or wherein the graphene fiber structure comprises a second metal layer on the first metal layer, preferably wherein the second metal layer comprises copper.

14 Graphene fiber structure according to claim 13, wherein the first metal layer has a first layer thickness which is in a range from 500 nm to 100 pm, and/or wherein the second metal layer has a second layer thickness which is in a range from 100 nm to 10 pm.

15. Graphene fiber structure according to one of claims 12 to 14, wherein the graphene fiber structure comprises a polymer layer between the plant leaf graphene core structure and the first metal layer, preferably wherein the polymer layer comprises chitosan.