Silver Nanoparticle-Assisted Electrochemically Exfoliated Graphene Inks Coated on PVA-Based Self-Healing Polymer Composites for Soft Electronics

Smart sensors with self-healing capabilities have recently aroused increasing interest in applications in soft electronics. However, challenges remain in balancing the sensors' self-healing and compatibility between their sensing and substrate layers. This study evaluated several self-healing polymer substrates and graphene ink-based strain-sensing coatings. The optimum electrochemically exfoliated graphene (e-graphene)/silver nanoparticle-coated tannic acid (TA)/superabsorbent polymer/graphene oxide (GO) blended poly(vinyl alcohol) polymer composites exhibited improvements of 47.1 and 39.2%, respectively, for the healing efficiency in a substrate crack area and in the graphene-based sensing layer due to conductive layer adhesion. While TA was found to improve healing efficiency on the coating surface by forming hydrogen bonds between the sensing and polymer layers, GO healed the polymer surface due to its ability to form bonds in the polymer matrix. The superabsorbent polymer was found to absorb excess water in e-graphene dispersion due to its host-guest interaction, while also reducing the coating thickness.

Fast Joule Heating for the Scalable and Green Production of Graphene with a High Surface Area

The rapid development of electric vehicles, unmanned aerial vehicles, and wearable electronic devices has led to great interest in research related to the synthesis of graphene with a high specific surface area for energy applications. However, the problem of graphene synthesis scalability, as well as the lengthy duration and high energy intensity of the activation processes of carbon materials, are significant disadvantages. In this study, a novel reactor was developed for the green, simple, and scalable electrochemical synthesis of graphene oxide with a low oxygen content of 14.1%. The resulting material was activated using the fast joule heating method. The processing of mildly oxidized graphene with a high-energy short electrical pulse (32 ms) made it possible to obtain a graphene-based porous carbon material with a specific surface area of up to 1984.5 m2/g. The increase in the specific surface area was attributed to the rupture of the original graphene flakes into smaller particles due to the explosive release of gaseous products. In addition, joule heating was able to instantly reduce the oxidized graphene and decrease its electrical resistance from >10 MΩ/sq to 20 Ω/sq due to sp2 carbon structure regeneration, as confirmed by Raman spectroscopy. The low energy intensity, simplicity, and use of environment-friendly chemicals rendered the proposed method scalable. The resulting graphene material with a high surface area and conductivity can be used in various energy applications, such as Li-ion batteries and supercapacitors.

Highly Washable and Conductive Cotton E-textiles Based on Electrochemically Exfoliated Graphene

In this study, cotton e-textiles were obtained using two types of graphene oxide. The first type of graphene oxide was synthesized using the Hummers' method. The second type was obtained by the electrochemical exfoliation of graphite in an ammonium salt solution. It was shown that e-textiles based on electrochemically exfoliated graphene have a higher electrical conductivity (2 kΩ/sq) than e-textiles based on graphene oxide obtained by the Hummers' method (585 kΩ/sq). In addition, textiles based on electrochemically exfoliated graphene exhibit better washing and mechanical stress stability. The electrical resistance of the e-textiles increased only 1.86 times after 10 cycles of washing, compared with 48 times for the Hummers' method graphene oxide textiles. The X-ray photoelectron spectra of the two types of graphene oxides showed similarity in their functional compositions after reduction. Studies of individual graphene flakes by atomic force microscopy showed that graphene oxide of the second type had a smaller lateral size. Raman spectroscopy showed a higher degree of sp² structure regeneration after reduction for the second type of graphene. These properties and the tendency to form agglomerated particles determine the mechanochemical stability and high electrical conductivity of e-textiles based on electrochemically exfoliated graphene.

Electrochemically Exfoliated Graphene for High-Durability Cement Composites

The development of radically new types of corrosion-resistant cement composites is nowadays compulsory in view of the continuous increase of concrete consumption combined with the intrinsically defective nature of concrete. Among various additives being employed in the concrete technology, carbon nanomaterials have emerged as extremely powerful components capable of remarkably enhancing nano- and microstructures as well as properties of cement-based composites. In this study, we demonstrate that cement mortar incorporating electrochemically exfoliated graphene (EEG) exhibits significantly improved fluid transport properties. The addition of 0.05 wt % of EEG to ordinary Portland cement mortar results in the reduction of initial and secondary sorptivity values by 21 and 25%, respectively. This leads to the outstanding resistance of EEG-cement composites to highly corrosive environments, namely, chloride and sulfate solutions. These observations, combined with the previously reported remarkable enhancement of the tensile strength of EEG-cement mortars, represent a major step toward the development of highly durable graphene-based cement composites.

Preparation of Nanocomposite-based High Performance Organic Field Effect Transistor via Solution Floating Method and Mechanical Property Evaluation

We demonstrate that using nanocomposite thin films consisting of semiconducting polymer, poly(3-hexylthiophene) (P3HT), and electrochemically exfoliated graphene (EEG) for the active channel layer of organic field-effect transistors (OFETs) improves both device performances and mechanical properties. The nanocomposite film was developed by directly blending P3HT solution with a dispersion of EEG at various weight proportions and simply transferring to an Si/SiO2 substrate by the solution floating method. The OFET based on P3HT/EEG nanocomposite film showed approximately twice higher field-effect mobility of 0.0391 cm²·V⁻¹·s⁻¹ and one order of magnitude greater on/off ratio of ~10⁴ compared with the OFET based on pristine P3HT. We also measured the mechanical properties of P3HT/EEG nanocomposite film via film-on-elastomer methods, which confirms that the P3HT/EEG nanocomposite film exhibited approximately 2.4 times higher modulus (3.29 GPa) than that of the P3HT film (1.38 GPa), while maintaining the good bending flexibility and durability over 10.0% of bending strain and bending cycles (1000 cycles). It was proved that the polymer hybridization technique, which involves adding EEG to a conjugated polymer, is a powerful route for enhancing both device performances and mechanical properties while maintaining the flexible characteristics of OFET devices.

High-Performance Graphene-Based Cementitious Composites

This study reports on the development of a cementitious composite incorporating electrochemically exfoliated graphene (EEG). This hybrid functional material features significantly enhanced microstructure and mechanical properties, as well as unaffected workability; thus, it outperforms previously reported cementitious composites containing graphene derivatives. The manufacturing of the composite relies on a simple and efficient method that enables the uniform dispersion of EEG within cement matrix in the absence of surfactants. Different from graphene oxide, EEG is found to not agglomerate in cement alkaline environment, thereby not affecting the fluidity of cementitious composites. The addition of 0.05 wt% graphene content to ordinary Portland cement results in an increase up to 79%, 8%, and 9% for the tensile strength, compressive strength, and Young's modulus, respectively. Remarkably, it is found that the addition of EEG promotes the hydration reaction of both alite and belite, thus leading to the formation of a large fraction of 3CaO·2SiO2·3H2O (C-S-H) phase. These findings represent a major step forward toward the practical application of nanomaterials in civil engineering.

Dual-Graphene Rechargeable Sodium Battery

Sodium (Na) ion batteries are attracting increasing attention for use in various electrical applications. However, the electrochemical behaviors, particularly the working voltages, of Na ion batteries are substantially lower than those of lithium (Li) ion batteries. Worse, the state-of-the-art Na ion battery cannot meet the demand of miniaturized in modern electronics. Here, we demonstrate that electrochemically exfoliated graphene (EG) nanosheets can reversibly store (PF₆^- ) anions, yielding high charging and discharging voltages of 4.7 and 4.3 V vs. Na⁺ /Na, respectively. The dual-graphene rechargeable Na battery fabricated using EG as both the positive and negative electrodes provided the highest operating voltage among all Na ion full cells reported to date, together with a maximum energy density of 250 Wh kg^-1 . Notably, the dual-graphene rechargeable Na microbattery exhibited an areal capacity of 35 μAh cm^-2 with stable cycling behavior. This study offers an efficient option for the development of novel rechargeable microbatteries with ultra-high operating voltage and high energy density.

Scalable Fabrication and Integration of Graphene Microsupercapacitors through Full Inkjet Printing

A simple full-inkjet-printing technique is developed for the scalable fabrication of graphene-based microsupercapacitors (MSCs) on various substrates. High-performance graphene inks are formulated by integrating the electrochemically exfoliated graphene with a solvent exchange technique to reliably print graphene interdigitated electrodes with tunable geometry and thickness. Along with the printed polyelectrolyte, poly(4-styrenesulfonic acid), the fully printed graphene-based MSCs attain the highest areal capacitance of ∼0.7 mF/cm², substantially advancing the state-of-art of all-solid-state MSCs with printed graphene electrodes. The full printing solution enables scalable fabrication of MSCs and effective connection of them in parallel and/or in series at various scales. Remarkably, more than 100 devices have been connected to form large-scale MSC arrays as power banks on both silicon wafers and Kapton. Without any extra protection or encapsulation, the MSC arrays can be reliably charged up to 12 V and retain the performance even 8 months after fabrication.

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

Micro-supercapacitors (MSCs) based on mesoporous polyaniline patterned graphene are demonstrated. The synergic effect from both electron-double-layer-capacitive graphene and pseudocapacitive mesoporous-polyaniline leads to outstanding MSC device performances, in regard to excellent volumetric capacitance and rate capabilities, which further result in a high power density of 600 W cm^-3 , suggesting opportunities for future portable and wearable power supplies in diverse applications.

A Quasi-Solid-State Li-Ion Capacitor Based on Porous TiO2 Hollow Microspheres Wrapped with Graphene Nanosheets

The quasi-solid-state Li-ion capacitor is demonstrated with graphene nanosheets prepared by an electrochemical exfoliation as the positive electrode and the porous TiO₂ hollow microspheres wrapped with the same graphene nanosheets as the negative electrode, using a Li-ion conducting gel polymer electrolyte. This device may be the key to bridging the gap between conventional lithium-ion batteries and supercapacitors, meanwhile meeting the safety demands of electronic devices.

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

A novel direct printing approach for fabrication of in-plane micro-supercapacitors (MSCs) is demonstrated. Solution-processed graphene/conductive-polymer hybrid inks are utilized. 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.

Transparent conductive electrodes from graphene/PEDOT:PSS hybrid inks for ultrathin organic photodetectors

A novel solution fabrication of large-area, highly conductive graphene films by spray-coating of a hybrid ink of exfoliated graphene (EG)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000) is demonstrated. The fabricated graphene films exhibit excellent mechanical properties, thus enabling their application as bottom electrodes in ultrathin organic photodetector devices with performance comparable to that of the state-of-the-art Si-based inorganic photodetectors.