Won G. Hong

One-step hydrothermal synthesis of graphene decorated V2O5 nanobelts for enhanced electrochemical energy storage

Graphene-decorated V2O5 nanobelts (GVNBs) were synthesized via a low-temperature hydrothermal method in a single step. V2O5 nanobelts (VNBs) were formed in the presence of graphene oxide, a mild oxidant, which also enhanced the conductivity of GVNBs. From the electron energy loss spectroscopy analysis, the reduced graphene oxide (rGO) are inserted into the layered crystal structure of V2O5 nanobelts, which further confirmed the enhanced conductivity of the nanobelts. The electrochemical energy-storage capacity of GVNBs was investigated for supercapacitor applications. The specific capacitance of GVNBs was evaluated using cyclic voltammetry (CV) and charge/discharge (CD) studies. The GVNBs having V2O5-rich composite, namely, V3G1 (VO/GO = 3:1), showed superior specific capacitance in comparison to the other composites (V1G1 and V1G3) and the pure materials. Moreover, the V3G1 composite showed excellent cyclic stability and the capacitance retention of about 82% was observed even after 5000 cycles.

A Novel Method for Applying Reduced Graphene Oxide Directly to Electronic Textiles from Yarns to Fabrics

Conductive, flexible, and durable reduced RGO textiles with a facile preparation method are presented. BSA proteins serve as universal adhesives for improving the adsorption of GO onto any textile, irrespective of the materials and the surface conditions. Using this method, we successfully prepared various RGO textiles based on nylon-6 yarns, cotton yarns, polyester yarns, and nonwoven fabrics.

Ultrasensitive and Highly Selective Graphene-Based Single Yarn for Use in Wearable Gas Sensor

Electric components based on fibers or textiles have been investigated owing to their potential applications in wearable devices. High performance on response to gas, drape-ability and washing durability are of important for gas sensors based on fiber substrates. In this report, we demonstrate the bendable and washable electronic textile (e-textile) gas sensors composed of reduced graphene oxides (RGOs) using commercially available yarn and molecular glue through an electrostatic self-assembly. The e-textile gas sensor possesses chemical durability to several detergent washing treatments and mechanical stability under 1,000 bending tests at an extreme bending radius of 1 mm as well as a high response to NO2 gas at room temperature with selectivity to other gases such as acetone, ethanol, ethylene, and CO2.

Effect of sulphur vacancy on geometric and electronic structure of MoS2 induced by molecular hydrogen treatment at room temperature

Investigations into the interaction between molecular hydrogen and molybdenum disulphide have been in increasing demand to improve the understanding of the hydrodesulphurisation process, especially the creation of sulphur vacancies which result in coordinatively unsaturated sites in MoS2. Here we present comprehensive studies of the structural and electronic modulation caused by exposure of MoS2 to H2 over a low temperature range, which may be helpful for industrial applications. Detail investigations were conducted with Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), and electrical transport properties as a function of H2 gas pressure up to 24 bar from 295 K to 350 K. Upon exposure to H2, we observed bond-softening using Raman spectroscopy, a decrease in d-spacing from the TEM results, and an increase in conductance, all of which are consistent with the first-principles calculations. The results demonstrate the formation of sulphur vacancies even under low H2 pressure at low temperature.

Electrical quadruple hysteresis in Pd-doped vanadium pentoxide nanowires due to water adsorption

Abstract Humidity-dependent current–voltage (I–V) characteristics of Pd-doped vanadium pentoxide nanowires (Pd-VONs) were investigated. Electrical quadruple hysteresis (QH) was observed and attributed to the large amount of water molecules adsorbed on the nanowires. Using QH in Pd-VONs, the reaction of water with PdO was interpreted as the water molecules are desorbed and then dissociated with increasing bias voltage. Owing to the dissociated H+ and OH− ions, PdO is reduced and oxidized. As a result, water molecules recombine as the bias voltage is decreased.

Pyroprotein‐Based Electronic Textiles with High Stability

Thermally reducible pyroprotein-based electronic textiles (e-textiles) are fabricated using graphene oxide and a pyroprotein such as cocoon silk and spider web without any chemical agents. The electrical conductivity of the e-textile is 11.63 S cm-1 , which is maintained even in bending, washing, and temperature variation.

Hydrogen spillover in Pd-doped V2O5 nanowires at room temperature.

Considerable efforts have been directed toward developing efficient hydrogen storage materials and finding methods to enhance the hydrogen storage capacity in order to meet the criteria set forth by the U.S. Department of Energy (DOE) toward hydrogen economy. Various carbon materials, metal hydrides, porous metal–organic frameworks (MOFs), and metal–polymer nanocomposites have been identified as promising candidates for hydrogen storage because they possess large surface areas, optimum interlayer distances of 6.0–7.0 , and strong interaction energies (~ 80 kJ mol ) between hydrogen and adsorbents. These are considered key factors for enhancing H2 storage capacity. In addition, the concept of hydrogen spillover has recently been revisited because an increase in H2 uptake was observed in a bridged MOF and Pd-decorated activated carbons containing surface oxygen functional groups via spillover. Spillover was first proposed to interpret the formation of tungsten bronze originating from the reduction of Pt-supported tungsten oxide. The spillover process has been proposed to proceed as follows. First, hydrogen molecules are chemisorbed on dispersed catalyst particles and dissociated, and the dissociated H atoms then migrate to the substrate and diffuse further. Despite extensive investigations, however, no consensus has been reached yet about the detailed mechanism and effects of hydrogen spillover. In the case of MoO3, different theoretical reports on the energetically most favorable position of H atoms on MoO3 after being spilled have been published. Chen et al. calculated that the strongest adsorption of hydrogen atoms occurs on the terminal oxygen of MoO3. [8] Adams reported that hydrogen atoms are adsorbed on different oxygen sites according to the hydrogen content. On the basis of first-principles calculations, Li et al. suggested that dissociated H atoms directly diffuse into sublayer oxygen atoms rather than into surface oxygen atoms. Chen et al. proposed, based on density functional theory calculations, that hydrogen can move freely on the surface and diffuse into the bulk lattice at ambient temperature. In this light, investigations of the final state of the supporting materials will guide the understanding of the spillover effect. Vanadium pentoxide nanowires (VONs) have attracted interest due to their versatile applications in the field of nanoelectronic devices. VONs have been considered for use in lithium-ion batteries, actuators, and sensors. An electrochromic property originating from the V to V reduction process due to Li insertion has also been reported. Similarly, if the spillover of hydrogen molecules occurs, we expected that an electrochromic change will be possible by introducing H atoms into VONs. Herein, we show that the color of Pd-doped VONs (Pd-VONs) changes from orange to black when H2 molecules are introduced at room temperature; the color does not revert to the original color, even after thermal annealing under vacuum at 673 K. To elucidate the H2 spillover effect, the state of Pd-VONs before and after H2 exposure was investigated by Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and an analysis of electrical transport properties. The data show that hydrogen molecules were first dissociated on Pd, followed by diffusion of H atoms into triply-coordinated oxygen in VONs. In this regard, we tentatively propose that hydrogen spillover of the Pd-doped V2O5 nanowires at relatively low temperature compared with bulk Pd/V2O5 composite [16] results from the improvement of catalytic property due to its nanosized structure. The Pd-VONs were prepared in accordance with the previously presented procedure. Figure 1 shows transmission [a] Prof. B. H. Kim, W. G. Hong, Dr. S. C. Jung, Dr. H. J. Kim Division of Materials Science Korea Basic Science Institute Daejeon 305-333 (Republic of Korea) E-mail : hansol@kbsi.re.kr [b] Dr. H. Y. Yu, Dr. J. Park Electronics and Telecommunications Research Institute Daejeon 305-333 (Republic of Korea) [c] Y. Nam, Prof. Y. W. Park Department of Physics and Astronomy Seoul National University Seoul 151-747 (Republic of Korea) [d] Prof. B. H. Kim, Prof. Y. Jun Interdisciplinary School of Green Energy, KIER-UNIST Center for Energy Ulsan National Institute of Science and Technology Ulsan 689-798 (Republic of Korea) E-mail : yjun@unist.ac.kr [e] Prof. H. Y. Jeong UNIST Central Research Facility and School of Mechanical and Advanced Materials Engineering Ulsan National Institute of Science and Technology Ulsan 689-798 (Republic of Korea) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201100947.

The Observation of electrical hysteric behavior in synthesized V 2 O 5 nanoplates by recrystallization

The anomalous electrical conductance for the V2O5 foam synthesized via a foaming process was measured. In the annealing process, the synthesized V2O5 foamis recrystallized with the increase of annealing temperature. The recrystallization procedure was characterized by using physical analysis tools such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffractometer. In the electrical analysis technique of current-voltage characteristics as a function of annealing temperature, an anomalous hysteric behavior appears at the annealing temperature of 400°C. We conclude that the recrystallization of V2O5 nanoplates results in the anomalous behavior in voltage-dependent current characteristics.

Highly stretchable, mechanically stable, and weavable reduced graphene oxide yarn with high NO2 sensitivity for wearable gas sensors

Stretchable gas sensors are important components of wearable electronic devices used for human safety and healthcare applications. However, the current low stretchability and poor stability of the materials limit their use. Here, we report a highly stretchable, stable, and sensitive NO2 gas sensor composed of reduced graphene oxide (RGO) sheets and highly elastic commercial yarns. To achieve high stretchability and good stability, the RGO sensors were fabricated using a pre-strain strategy (strain-release assembly). The fabricated stretchable RGO gas sensors showed high NO2 sensitivity (55% at 5.0 ppm) under 200% strain and outstanding mechanical stability (even up to 5000 cycles at 400% applied strain), making them ideal for wearable electronic applications. In addition, our elastic graphene gas sensors can also be woven into fabrics and clothes for the creation of smart textiles. Finally, we successfully fabricated wearable gas-sensing wrist-bands from superelastic graphene yarns and stretchable knits to demonstrate a wearable electronic device.