Graphene Core 1 Graphene-Based Disruptive Technologies ... · 5 hybrid film was obtained through facile vacuum filtration of a dispersion of EG and V 2O 5 mixture (mass ratio = 4:1)

Project funded by the European Commission under Grant Agreement n°696656

Graphene Core 1 Graphene-Based Disruptive Technologies

Horizon 2020 RIA

WP13 Functional Foams and Coatings Deliverable 13.1 “Composite thin films for electronic

and energy-related applications”

Main Author(s): Martin R. Lohe, Xinliang Feng - Technische Universität Dresden

Due date of deliverable: M12 Actual submission date: M12 Dissemination level: PU

Graphene Core 1 D13.1 31 March 2017 2 / 15

List of Contributors Partner Acronym Partner Name Name of the contact

44 TUD Technische Universität Dresden Xinliang Feng 27 UdS Université de Strasbourg Paolo Samori

28 UCAM The Chancellor, Masters and Scholars of the University of Cambridge

Andrea C. Ferrari

94 TECNALIA Fundacion Tecnalia Research & Innovation Yolanda Belaustegi

120 INFN Istituto Nazionale di Fisica Nucleare Stefano Bellucci

29 MPG Max Planck Gesellschaft zur Foerderung der Wissenschaften E.V.

Klaus Müllen


TABLE OF CONTENTS

List of Contributors ................................................................................................... 2

Summary .................................................................................................................... 4

Introduction ................................................................................................................ 4

1. Preparing and testing of G and GRM -based composite coatings .............. 41.1 Electrochemical Exfoliation of Black Phosphorus ................................................ 41.2 Electrochemical Exfoliation of MoS2 ....................................................................... 51.3 Hybrid Films from Graphene Exfoliated in the Presence of Polymers ................ 5

2. Composite thin films for energy-related applications .................................. 62.1 Heterostructure Coatings of 2D Polythiophene Nanosheets and Graphene for High-Rate All-Solid-State Pseudocapacitors .................................................................... 62.2 Stimulus-Responsive Micro-Supercapacitors with Ultrahigh Energy Density and Reversible Electrochromic Window ........................................................................... 62.3 High Power In-Plane Micro-Supercapacitors Based on Mesoporous Polyaniline Patterned Graphene ............................................................................................................ 72.4 A Lyotropic Liquid-Crystal-Based Assembly of Highly Oriented V2O5/G Films for Flexible Energy Storage ............................................................................................... 82.5 Ultraflexible In-Plane Micro-Supercapacitors by Direct Printing of Solution-Processable Electrochemically Exfoliated Graphene ..................................................... 82.6 Facile Template-Free Synthesis of Vertically Aligned Polypyrrole Nanosheets on Nickel Foams for Flexible All-Solid-State Asymmetric Supercapacitors ................. 92.7 Flexible All-Solid-State Supercapacitors Boosted by Solution Processable MXene and Electrochemically Exfoliated Graphene ...................................................... 102.8 Electrochemical Exfoliation of G/TiS2 for Supercapacitor Electrodes ............... 102.9 Hybrid Silicon Nanoparticle/Graphene Inks for Battery Applications ................ 102.10 Electrodes for Capacitive Desalination ................................................................. 102.11 Immobilizing Molecular Metal Dithiolene–Diamine Complexes on 2D Metal–Organic Frameworks for Electrocatalytic H2 Production .............................................. 11

3. GRM- and Composite Coatings for Use in Electronic Applications .......... 123.1 EMI Shielding ........................................................................................................... 123.2 Graphene/Quantum-Dot Composite Films for Luminescent Devices ................ 133.3 Inks for Printed Electronics .................................................................................... 13

Conclusions ............................................................................................................. 14

References ............................................................................................................... 14


Summary

The excellent solution-processability of two-dimensional (2D) materials can benefit various applications and via chemical approaches we have fine-tuned these materials to work in high-performance devices. Especially the combination of graphene with other materials, such as 2D polymers, which individually own unique features complimentary to the outstanding properties of graphene, has led to exciting scientific achievements. This report introduces recent progress of such graphene-based hybrids and other 2D materials in the field of energy storage and conversion, as well as new scaleable protocols to obtain black phosphorus (BP) flakes and MoS2 with good quality and novel strategies to develop integrated thin-films and coatings for electronics and catalysts.

Introduction The first part of this report is presenting new scalable, electrochemical production protocols towards the exfoliation of black phosphorus and molybdenum disulphide bulk materials, which are promising components for future hybrid inks and coating materials as they are able to expand the available spectrum of properties that can be achieved by using graphene-based nanocomposite coatings. The second part focusses on different approaches towards hybrid nanocomposite coatings for use in energy storage devices that are able to significantly increase the performance over state of the art devices or introduce new functionalities such as flexibility or environmental response. In the third and last part, we focus on recent developments in the development of coatings for electronic applications, such as conductive inks with improved performance.

1. Preparing and testing of G and GRM -based composite coatings 1.1 Electrochemical Exfoliation of Black Phosphorus

TUD developed an efficient protocol to exfoliate black phosphorus (BP) crystal into thin layers with high yield (~ 60 %) by electrochemical method (Figure 1). The overall exfoliation process completes within 60 min. The exfoliated BP flakes exhibit large dimension ranging from 1 to 5 µm and average thickness of 1.70 nm, which is in accordance with trilayer-BP. The investigation of the electronic properties of BP is ongoing.

Figure 1: Schematic setup (top left) of exfoliation chamber using BP crystal in an organic electrolyte. Pictures taken at 0 min and after 60 min (bottom left) show the efficient exfoliation of BP. SEM, TEM and AFM have been employed for characterisation (right)


1.2 Electrochemical Exfoliation of MoS2 TUD demonstrated the delamination of MoS2 crystal into two-dimensional flakes in organic electrolytes (Fig. 2). When MoS2 crystal serves as cathode, the exfoliation occurs once an external DC bias is applied. The resulted MoS2 flakes show good dispersibility in DMF, affording a stable dispersion with concentration of 0.5 mg/ml, stable for 2 weeks without apparent aggregation. TEM images reveal multilayer structure. Lattice defects are not visible under high-resolution TEM, indicating good quality of MoS2 flakes. This method would be valuable for scaled-up production of high-quality MoS2 sheets.

1.3 Hybrid Films from Graphene Exfoliated in the Presence of Polymers UDS reported earlier that blending of OSCs with graphene prior to deposition can lead to improvements of the performances of PNDI2OD-T2’s p-type transport performances.1 In 2015, UDS reported tuneable transport regimes in films produced by successive depositions of graphene and OSCs.2 The focus of the current project is on the combination of the materials at the earliest possible stage of fabrication, the exfoliation step. The graphene/polymer dispersion was prepared by Ultrasounds Induced Liquid-Phase Exfoliation (UILPE) of graphite in a polymer (P3HT or PCD-TPT) solution in 1,2-dichlorobenzene under nitrogen atmosphere. The dispersion was spin-coated on silicon oxide substrates pre-patterned pairs of gold electrodes. Fabrication steps are summarized in (Figure 3). OFET properties were evaluated under negative gate bias in nitrogen atmosphere. Unlike pristine graphene and graphene exfoliated in the presence of P3HT, graphene exfoliated in the presence of PCDTPT lead to homogeneous films with a high concentration of few-layer graphene flakes without large

Figure 2: Scheme (top) of MoS2 delamination. Pictures of the exfoliation process and dispersion of MoS2 in DMF (middle). TEM and high-resolution TEM of MoS2 flake (down).

Figure 3: Fabrication of hybrid LPE-graphene/polymer films. Schematic representation of (a) graphite in the presence of the polymer solution, (b) graphene dispersion after ultrasound induced exfoliation and (c) the film resulting from spin-coating of the graphene deposition. The film is used as the active material of a bottom-gate bottom-contact transistor.


graphitic aggregates indicating that PCDTPT plays an active role in the exfoliation process and not only the deposition. The mobility of the films was measured to exceed 0.1 cm²/Vs, a 30-fold increase over pure PCDTPT films. These findings are a gateway to optimization of graphene exfoliation, deposition and performance increase, as they highlight the importance of the selection of an adequate polymer added before the exfoliation of 2D-materials. These findings are a gateway to optimization of graphene exfoliation and deposition, as they highlight the importance of the selection of an adequate polymer added before the exfoliation of 2D-materials.

2. Composite thin films for energy-related applications 2.1 Heterostructure Coatings of 2D Polythiophene Nanosheets and Graphene

for High-Rate All-Solid-State Pseudocapacitors TUD in collaboration with MPIP produced stacked-layer heterostructure coatings of 2D polythiophene nanosheets and graphene. The stacked-layer heterostructure films were fabricated from thiophene (TP) nanosheets and electrochemically exfoliated graphene (EG) by alternated deposition of EG nanosheets (≤3 layers) and redox-active, conducting TP nanosheets (thickness of 3.5 nm), and exhibit large-area uniformity. The produced coatings were directly transferred on a polyethylene terephthalate substrate and served as binder- and additive-free electrodes for flexible all-solid-state supercapacitors (ASSS).3 The TP/EG-ASSSs showed high areal capacitance of 3.9 mF cm−2 at 1 mV s−1 and good rate capability (2.4 mF cm−2 at 500 mV s−1). Accordingly, the TP/EG-ASSSs delivered an ultrahigh volumetric capacitance of ≈375 F cm−3 and a significant volumetric capacitance of 62 F cm−3 even at 100 V s−1, which can be attributed to the synergetic effect of the ultrathin pseudocapacitive thiophene nanosheets and the capacitive electrochemically exfoliated graphene. These results further demonstrate the essential merits of the unique heterostructure coatings for energy storage.

2.2 Stimulus-Responsive Micro-Supercapacitors with Ultrahigh Energy Density and Reversible Electrochromic Window

Hybrid coatings of vanadium pentoxide and electrochemical exfoliated graphene (EG) have been produced at TUD. The EG nanosheets and V2O5 nanoribbons were first prepared using an electrochemical exfoliation method and a hydrothermal method, respectively. The EG/V2O5 hybrid film was obtained through facile vacuum filtration of a dispersion of EG and V2O5 mixture (mass ratio = 4:1). Subsequently, the hybrid thin-film was transferred onto transparent substrates such as rigid glass slide or flexible polyethylene terephthalate (PET)

Figure 4: SEM micrograph of hybrid stacked EG/TP hetero-structure, and thin film on flexible PET-substrate (insert).

Figure 5: Semi-transparent hybrid EG/V2O5 coating on flexible PET film (a) and SEM cross-section image of a hybrid coating on glass substrate (b).


film.4 Taking advantage of the synergistic effect of 1D V2O5 nanoribbons and 2D exfoliated graphene (EG) nanosheets, EG/V2O5 hybrid nanopaper was prepared as electrode for micro-supercapacitors (MSCs), which delivered a high volumetric capacitance of 130.7 F cm−3 at 10 mV s−1 with a polyvinyl alcohol (PVA)/LiCl gel electrolyte. Notably, the volumetric energy density was ≈20 mWh cm−3 (power density = 235 W cm−3), which is markedly higher than the energy densities of the state-of-the-art MSCs. After solidification of the electrolyte together with methyl viologen, the resulting stimuli responsive MSCs manifested a remarkable reversible electrochromic effect during the charge-discharge process within 0-1 V, which provides a direct visual observation of the charge-discharge state of the MSCs.

2.3 High Power In-Plane Micro-Supercapacitors Based on Mesoporous Polyaniline Patterned Graphene

Mesoporous polyaniline patterned graphene was produced at TUD and MPIP as shown in Figure 6. Graphene was prepared by electrochemical exfoliation of graphite foil as previously reported. Subsequently, the EG was non-covalently functionalised with 1-pyrenesulfonic acid sodium salt (PSA) via π–π interactions between the pyrene moiety of PSA and graphene. The surface of EG was thus negatively charged with the sulfonyl group of PSA, rendering its improved aqueous dispersion. Next, amphiphilic block copolymer polystyrene-b-poly(ethylene oxide) (PS146-b-PEO117) mono-micelles (self-assembled in THF/H2O mixed solvent, in spherical shape with a diameter of 20 nm) were assembled and anchored on PSA-functionalized EG surface, followed by addition and polymerization of aniline along PS146-b-PEO117 micelles to form mesoporous polyaniline (PANi) on both sides of the EG. At last, the copolymer templates were removed by repeated washing with THF, and the obtained EG/mPANi sheets could be stably dispersed in 2-propanol (IPA) at a concentration of 1 mg mL−1.5 The microsupercapacitors (MSCs) based on mesoporous polyaniline patterned graphene have been demonstrated. The synergistic effect from both electron-double-layer-capacitive graphene and pseudocapacitive mesoporous-polyaniline leads to outstanding MSC device performances including excellent volumetric capacitance and rate capabilities. Remarkably, a

Figure 6: Schematic preparation pathway toward mesoporous PANi-coated EG sheets.


maximum areal capacitance of 1.5 mF cm−2 and a volumetric capacitance of 75 F cm−3 were achieved at a scan rate of 10 mV s−1. Moreover, at ultrahigh scan rate of 106 mV s−1, a 500-nm thick EG/mPANi-coating MSC furnished a high power density of 600 W cm−3.

2.4 A Lyotropic Liquid-Crystal-Based Assembly of Highly Oriented V2O5/G

Films for Flexible Energy Storage TUD produced composite thin films of vanadium pentoxide (V2O5) nanobelts and graphene oxide (GO) sheets as shown in Figure 7. A novel lyotropic liquid-crystal (LC) based assembly strategy has been developed for the first time, to fabricate composite films of vanadium pentoxide (V2O5) nanobelts and graphene oxide (GO) sheets with highly oriented, layered structures. It was found that lamellar LC phases can be simply established by V2O5 nanobelts alone or by a mixture of V2O5 nanobelts and GO nanosheets in their aqueous dispersions. More importantly, the LC phases can be retained with any proportion of V2O5 nanobelts and GO, which allows facile optimization of the ratio of each component in the resulting films. The so called VrGO composite films show high electrical conductivity, good mechanical stability, and excellent flexibility, which allow them to be utilized as high performance electrodes in flexible energy storage devices (Figure 8).6 As demonstrated in this work, the VrGO films containing 67 wt% V2O5

exhibit excellent capacity of 166 F g−1 at 10 A g−1, which is superior to those of the previously reported composites of V2O5 and nanocarbon.

2.5 Ultraflexible In-Plane Micro-Supercapacitors by Direct Printing of Solution-Processable Electrochemically Exfoliated Graphene

MPIP and TUD fabricated a hybrid ink, composed of electrochemically exfoliated graphene (EG) and an electrochemically active PEDOT:PSS formulation. By spray-coating the EG/PEDOT:PSS hybrid ink through a shadow mask with the designed MSC device geometry, the direct printing of MSCs was realized (Figure 9).7 Thus, a novel direct printing approach for the fabrication of in-plane micro-supercapacitors was demonstrated by utilising solution-

Figure 7: Preparation scheme towards hybrid V2O5 nanobelt/GO coatings and foams.

Figure 8: VrGO-based supercapacitor powering an LED (left) and photographs showing the excellent flexibility of VrGO-coatings (middle, right).


processed graphene/conductive-polymer hybrid inks. The fabricated MSCs on paper substrates offer significant areal capacitance and excellent rate capability. An ultrathin MSC on a poly(ethylene terephthalate) (PET) substrate (2.5 μm thick) exhibits “ultraflexiblity,” making it suitable for next-generation flexible microelectrochemical energy-storage devices. The fabricated MSCs on paper substrates offered a significant areal capacitance as high as 5.4 mF cm−2, which is superior to that of state-of-the-art graphene-based MSCs.

2.6 Facile Template-Free Synthesis of Vertically Aligned Polypyrrole Nanosheets on Nickel Foams for Flexible All-Solid-State Asymmetric Supercapacitors

Vertically aligned PPy nanosheets on Ni foams have been prepared at TUD. A novel and remarkably facile approach towards vertically aligned nanosheets on 3D-Ni foams was developed. Conducting polypyrrole (PPy) sheets were grown on Ni foam through the volatilisation of the environmentally friendly solvent from an ethanol-water solution of pyrrole (Py), followed by the polymerisation of the coated Py in ammonium persulfate (APS) solution (Figure 10). The PPy-decorated Ni foams and commercial activated carbon (AC) modified Ni foams were employed as the two electrodes for the assembly of flexible all-solid-state asymmetric supercapacitors.8 The PPy-coated Ni foams and AC modified Ni foams were employed as the two electrodes for the assembly of PPy–Ni//AC–Ni flexible all-solid-state asymmetric supercapacitors (Figure 11). The PPy-Ni//AC-Ni capacitor device exhibited a high specific capacitance of up to 38 F g−1 at 0.2 A g−1 and good cycling stability with ∼82% capacitance retention after 2000 cycles. Moreover, a high energy density of ∼14 Wh kg−1 and a power density of 6.2 kW kg−1 were achieved for the flexible all-solid-state supercapacitors.

Figure 9: Deposition process for direct printing of EG/PEDOT:PSS inks and resulting MSC device.

Figure 10: Preparation scheme of vertically aligned PPy nanosheets on Ni foams.

Figure 11: Configuration of the asymmetric supercapacitor device.


2.7 Flexible All-Solid-State Supercapacitors Boosted by Solution Processable MXene and Electrochemically Exfoliated Graphene

TUD has developed a hybrid film of MXene nanosheets and electrochemically exfoliated graphene (EG). Graphene was prepared from electrochemically exfoliation of graphite foil and Mxene was prepared via a HF-etching method. A hybrid ink was then produced by ultrasonication of EG-Mxene mixture in a weight ratio of 1:3. After filtration of the hybrid ink, a free-standing hybrid thin film of EG and Mxene was formed (Figure 12). Flexible all-solid-state supercapacitors and in-plane micro-supercapacitors based on MXene and exfoliated graphene are fabricated with ultrahigh volumetric capacitances.9 The fabricated ASSS device exhibited outstanding volumetric capacitance of up to 216 F cm−3 at 0.1 A cm−3.

2.8 Electrochemical Exfoliation of G/TiS2 for Supercapacitor Electrodes UCAM developed a new coating for supercapacitor applications based on the heterogeneous structure of graphene and TiS2 nanoplatelets. The ink was prepared by co-exfoliation of the bulk materials using the electrochemical method in an organic solvent. The exfoliated material was washed with ethanol, and a paste was formed by adding NMP and PTFE as a binder. This was then coated on Ni foam and dried overnight under vacuum. We used these coated samples as electrodes for symmetrical supercapacitors. The measured areal capacitance is 17.1 mF cm-2. The electrochemical device showed high rate and good stability after 10000 cycles of charging and discharging.10

2.9 Hybrid Silicon Nanoparticle/Graphene Inks for Battery Applications UCAM achieved 1200 mAh g-1

electrode at 400 mA g-1electrode by developing electrically conductive

Si-graphene composites from silicon-graphene inks. UCAM developed an electrode composed of silicon nanoparticles (SiNPs) and flakes. Electrodes with areal densities of 1–3 mg cm-2 show a reversible gravimetric capacity of 2000–2500 mAh g-1

electrode at a rate of 400 mA g-1

electrode, with a first cycle Coulombic efficiency of 86-88% and an areal capacity of 2-4 mAh cm-2. The gravimetric capacity is 10 times greater than graphite electrodes, and the areal capacity meets the value required for commercial viability. As the areal capacity depends on the electrode thickness and areal density, it is possible to increase the areal capacity beyond the 4 mAh cm-2 benchmark. For an electrode with a thickness of 25 μm, a volumetric capacity of 1200 mAh cm-3 was obtained. The rate performance of the Si-flake electrode, a measure of the current density during charge and discharge of the electrode, shows that the electrode could be cycled up to 1200 mA g-1 while yielding a large capacity of 1500 mAh g-1.11

2.10 Electrodes for Capacitive Desalination TECNALIA has developed new hybrid materials for CDI electrodes based on 3D-graphene coatings with metallic salts with high capacitance values (>200 F g-1) and good electrosorption

Figure 12: TEM (a) and SEM (b) images of hybrid EG/MXene films.


capacity values of sodium and chloride ions (Figure 13). The synthesis process has been optimised and validated in the laboratory. Currently, TECNALIA is scaling up this synthesis method to increase the production of 3D-graphene materials while keeping their properties. Also, TECNALIA is studying the production process of larger electrodes than 3x3 cm. For the time being, the used techniques are tape casting and screen printing. The production of 3D graphene coatings with metallic salts and electrodes at higher scale are being studied. As a consequence, a new CDI desalination lab-scale device will be constructed in order to test larger electrodes. The electrode performance will be tested with synthetic seawater, not only with artificial NaCl solution in order to prove the performance under more realistic conditions. The adsorption performance obtained by newly synthesised graphene electrodes is much higher than actual state of the art carbon electrodes. However, further work in more realistic conditions is required in order to confirm the high potential of this new desalination system. Tecnalia and Polymem are working in a coordinated way on the design and construction of the up-scaled CDI prototype. Graphenea provided graphene oxide aqueous solutions, which were the basic material of the developed new electrode compositions. UCAM provided some water based conductive graphene ink and graphene oxide aqueous solutions for the fabrication of electrodes, which were tested in the capacitive deionization device. Also, Grupo Antolín provided graphene oxide aqueous solutions.

2.11 Immobilizing Molecular Metal Dithiolene–Diamine Complexes on 2D Metal–Organic Frameworks for Electrocatalytic H2 Production

The direct usage of metal-organic coordination frameworks (MOFs) as electrocatalysts for hydrogen production in water is still challenging due to its typical poor conductivity and low mechanical stability. In recent work, TUD demonstrated the fabrication of a novel 2D-MOF single-layer sheet (~0.7 nm in thickness, and >1 cm2 size) consisting of nickel bis(dithiolene) complexes (NiS4) at the air/water interface by the LB method (Figure 14a). Such 2D MOFs can serve as promising carbon-rich electrocatalysts owing to the following advantages: (I) the fully π-conjugated 2D MOF films present high conductivity (~150 S cm-1); (II) the 2D MOF surface allows for sufficient exposure of the catalytically active sites; (III) the molecular catalytic sites are immobilized onto solid-state materials to prevent loss of their stability and reactivity in aqueous solution. Here, the THT-Ni sheets allow for the sufficient exposure of well-distributed nickel bis(dithiolene) moieties, leading to a highly efficient electrocatalytic hydrogen evolution reaction (HER) with a Tafel slope of 80.5 mV decade-1, an onset overpotential of 110 mV and an operating overpotential of 333 mV at 10 mA cm-2 (Figure 14b), which are superior to those

Figure 13: SEM micrographs of the improved CDI electrodes based on 3D-graphene coatings decorated with metallic salts.


of recently reported carbon nanotube (CNT)-supported molecular catalysts and heteroatom-doped graphene catalysts. Therefore, this work provides an appealing strategy for the rational construction of large-area, free-standing 2D MOF nanosheets for energy conversion.12

3. GRM- and Composite Coatings for Use in Electronic Applications

3.1 EMI Shielding INFN investigated the possibility of GRM to be used in a wide range of applications, focusing on electronics and energy fields. In the field of electromagnetic shielding, a GNP (Graphene NanoPlatelets) thin film was used for a tuneable attenuator device. The GNP patch was deposited in two configurations, first in the gap of a microstrip line and secondly, as a novel enhanced design, two graphene patches located between the main microstrip line and two metal vias. The results show a wide band functionality from DC to 20 GHz, with a tuneability

Figure 15: Geometry of the graphene-based tunable microstrip attenuator and bias voltage vs. graphene resistance (right) for two configurations: (a) Preliminary microstrip attenuator with the graphene pad located in a gap of the microstrip line. (b) Enhanced microstrip attenuator with symmetrical graphene pads, located between the microstrip line and grounded vias.

Figure 14: (a) Synthesis of a 2D MOF single-layer sheet at an air/water interface. (b) HER polarization plots of the NiS4 2D MOF sheet in 0.5 M H2SO4. The inset in (b) shows the corresponding Tafel plot.


of 7 dB and minimum insertion loss of 5 dB for the first configuration, and an operation in a frequency band of DC to 5 GHz, with 14 dB tuneability and minimum insertion loss of 0.3 dB for the second configuration.13

3.2 Graphene/Quantum-Dot Composite Films for Luminescent Devices For electronic applications, INFN has produced three phase composites. In a first approach GNPs were decorated with copper nanoparticles dispersed in poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS) as conducting polymer matrix.14 The obtained composite has good film forming properties and resistance (of about 380 Ω). The proposed low-temperature solution process opens a feasible approach to manufacturing of low-cost transparent (in the case of very thin films) and conductive electrodes. A second approach in this field is regarding the possible interactions between GNP and quantum dots. The interest in graphene-quantum dot composites is caused by the possibility to combine high absorption ability of quantum dots with high charge carrier mobility in graphene, which are of great importance for many electronic devices. INFN has studied two systems: (i) CdSe nanoplatelets with graphene nanoplatelets in poly-N-epoxypropylcarbazole and (ii) CdSe spherical nanoparticles with graphene nanoplatelets in MEH-PPV.15 Two maxima in the luminescence spectra of CdSe nanoplatelets were found, based on efficient absorption of photons between the neighbouring nanoplatelets. It was found that luminescence of the samples was weak both for polymer and nanoparticles indicating the luminescence quenching. Moreover, the luminescence of the active particles was found to be different in various places of the sample, being strongly dependent on the graphene type (stronger luminescence was observed in graphene with smaller number of defects). These results should be taken into account in the design of luminescent devices for energy applications. Finally, the charge scattering from spatially asymmetric antidots patterned on graphene has been investigated, in the ballistic scale. This work can be the basis for a systematic study of the Ratchet effect in the above kind of structure. A completely deterministic characterization of this effect was proposed, based on the scattering of asymmetric defects under external electromagnetic excitation. The Ratchet effect could be usefully exploited to realize high frequency detectors, sensors, and harvesting devices.16

3.3 Inks for Printed Electronics UCAM optimised the composition of water based screen-printable graphene inks to produce thicker coatings with lower sheet resistance. UCAM increased the solids content by increasing the flakes concentration to 100 g/L in the microfluidic process. Since microfluidisation offers uniform high shear processing, UCAM utilised all the exfoliated flakes for the ink formulation (yield by weight =100%). UCAM optimised the concentration of the SDC surfactant. The minimum amount is 5 g/L (ratio exfoliated flakes/surfactant: 20:1). Following microfluidisation, carboxymethyl cellulose was added at a concentration of 10 g/L to increase the viscosity and induce a thixotropic character to the ink making it ideal for screen printing. The optimised ink formulation was tested using a semiautomatic flatbed screen printer Kippax kpx 2012 and a Natgraph industrial screen printer both equipped with screens with 120 mesh count per inch. Without any further modification to the ink, UCAM demonstrated large area printing of 29×29 cm2 on paper substrates with a line resolution ~100 μm. UCAM prepared >3 L ink and screen printed >200 capacitive touchpad posters using an industrial printer. These were used for outreach at the Mobile World Congress 2017 in


Barcelona. Some were distributed to visitors and others were used at a parallel event - YoMo (Youth Mobile). Moreover, the ink was tested as electrode in dye sensitised solar cell modules (~8 cm2) in collaboration with WP11, and showed similar performance to standard silver metal electrodes, but with enhanced stability over silver. For applications where water is not permitted, UCAM formulated an ink based on organic solvents. In this approach, UCAM microfluidised graphite in isopropanol using ethyl cellulose as a dispersing agent. Following microfluidisation, UCAM performed high speed centrifugation to sediment all the exfoliated material and exchanged isopropanol with cellosolve solvent. The flakes were redispersed in cellosolve by mechanical stirring. We used a cellulose ether (methocel) to induce a thixotropic behaviour to the dispersion and stabilise the flakes against sedimentation. UCAM reached a sheet resistance of 1.2 Ω/o after post deposition mechanical polishing of blade coated films.17

Conclusions We have shown recent progress of graphene-based hybrid films with new structures or compositions and their properties in the field of energy storage, conversion and electronics. Graphene flakes with mesoporous polymers, metal oxides, -sulphides or -carbides enable outstanding performance in supercapacitors and batteries. In particular, by using ink-jet printing or coating, we have demonstrated the possibility to fabricate devices on a large scale. Moreover, other 2D materials, such as 2D metal-organic frameworks were uncovered as promising candidates for catalytic reactions (e.g. water splitting). In addition, we have illustrated some preliminary results on the production of other 2D materials beyond graphene that will benefit the development of future nanohybrid coatings. More attention will be given to multifunctional devices, novel materials, and new technologies for device fabrications.

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Graphene Core 1 Graphene-Based Disruptive Technologies ... · 5 hybrid film was obtained through facile vacuum filtration of a dispersion of EG and V 2O 5 mixture (mass ratio = 4:1)