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Showing papers in "Advanced Functional Materials in 2015"


Journal ArticleDOI
TL;DR: In this article, recent exciting progresses on CD and GQD-based optoelectronic and energy devices, such as light emitting diodes (LEDs), solar cells (SCs), photodetctors (PDs), photocatalysis, batteries, and supercapacitors are highlighted.
Abstract: As new members of carbon material family, carbon and graphene quantum dots (CDs, GQDs) have attracted tremendous attentions for their potentials for biological, optoelectronic, and energy related applications. Among these applications, bio-imaging has been intensively studied, but optoelectronic and energy devices are rapidly rising. In this Feature Article, recent exciting progresses on CD- and GQD-based optoelectronic and energy devices, such as light emitting diodes (LEDs), solar cells (SCs), photodetctors (PDs), photocatalysis, batteries, and supercapacitors are highlighted. The recent understanding on their microstructure and optical properties are briefly introduced in the first part. Some important progresses on optoelectronic and energy devices are then addressed as the main part of this Feature Article. Finally, a brief outlook is given, pointing out that CDs and GQDs could play more important roles in communication- and energy-functional devices in the near future.

1,023 citations


Journal ArticleDOI
TL;DR: In this paper, a high-performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high-pressure solid-phase compression molding.
Abstract: A high-performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high-pressure solid-phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi-facet segregated architecture with rGO selectively located on the boundaries among PS multi-facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional-pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.

968 citations


Journal ArticleDOI
TL;DR: Holey GCN (HGCN) as mentioned in this paper is a self-modified graphitic carbon nitride nanosheets with abundant in-plane holes by thermally treating bulk GCN under an NH3 atmosphere.
Abstract: 2D graphitic carbon nitride (GCN) nanosheets have attracted tremendous attention in photocatalysis due to their many intriguing properties. However, the photocatalytic performance of GCN nanosheets is still restricted by the limited active sites and the serious aggregation during the photocatalytic process. Herein, a simple approach to produce holey GCN (HGCN) nanosheets with abundant in-plane holes by thermally treating bulk GCN (BGCN) under an NH3 atmosphere is reported. These formed in-plane holes not only endow GCN nanosheets with more exposed active edges and cross-plane diffusion channels that greatly speed up mass and photogenerated charge transfer, but also provide numerous boundaries and thus decrease the aggregation. Compared to BGCN, the resultant HGCN has a much higher specific surface area of 196 m2 g−1, together with an enlarged bandgap of 2.95 eV. In addition, the HGCN is demonstrated to be self-modified with carbon vacancies that make HGCN show much broader light absorption extending to the near-infrared region, a higher donor density, and remarkably longer lifetime of charge carriers. As such, HGCN has a much higher photocatalytic hydrogen production rate of nearly 20 times the rate of BGCN.

820 citations


Journal ArticleDOI
TL;DR: In this article, a basic N-methyl-2-pyrrolidone (NMP) liquid exfoliation method is described to produce phosphorene with excellent water stability, controllable size and layer number, as well as in high yield.
Abstract: Although phosphorene has attracted much attention in electronics and optoelectronics as a new type of two-dimensional material, in-depth investigations and applications have been limited by the current synthesis techniques. Herein, a basic N-methyl-2-pyrrolidone (NMP) liquid exfoliation method is described to produce phosphorene with excellent water stability, controllable size and layer number, as well as in high yield. Phosphorene samples composed of one to four layers exhibit layer-dependent Raman scattering characteristics thus providing a fast and efficient means for the in situ determination of the thickness (layer number) of phosphorene. The linear and nonlinear ultrafast absorption behavior of the as-exfoliated phosphorene is investigated systematically by UV–vis–NIR absorption and Z-scan measurements. By taking advantage of their unique nonlinear absorption, ultrashort pulse generation applicable to optical saturable absorbers is demonstrated. In addition to a unique fabrication technique, our work also reveals the large potential of phosphorene in ultrafast photonics.

820 citations


Journal ArticleDOI
TL;DR: In this article, the photoluminescence, transmittance, charge-carrier recombination dynamics, mobility, and diffusion length of CH3NH3PbI3 were investigated in the temperature range from 8 to 370 K.
Abstract: The photoluminescence, transmittance, charge-carrier recombination dynamics, mobility, and diffusion length of CH3NH3PbI3 are investigated in the temperature range from 8 to 370 K. Profound changes in the optoelectronic properties of this prototypical photovoltaic material are observed across the two structural phase transitions occurring at 160 and 310 K. Drude-like terahertz photoconductivity spectra at all temperatures above 80 K suggest that charge localization effects are absent in this range. The monomolecular charge-carrier recombination rate generally increases with rising temperature, indicating a mechanism dominated by ionized impurity mediated recombination. Deduced activation energies Ea associated with ionization are found to increase markedly from the room-temperature tetragonal (Ea ≈ 20 meV) to the higher-temperature cubic (Ea ≈ 200 meV) phase adopted above 310 K. Conversely, the bimolecular rate constant decreases with rising temperature as charge-carrier mobility declines, while the Auger rate constant is highly phase specific, suggesting a strong dependence on electronic band structure. The charge-carrier diffusion length gradually decreases with rising temperature from about 3 μm at -93 °C to 1.2 μm at 67 °C but remains well above the optical absorption depth in the visible spectrum. These results demonstrate that there are no fundamental obstacles to the operation of cells based on CH3NH3PbI3 under typical field conditions. The photoconductivity in CH3NH3PbI3 thin films is investigated from 8 to 370 K across three structural phases. Analysis of the charge-carrier recombination dynamics reveals a variety of starkly differing recombination mechanisms. Evidence of charge-carrier localization is observed only at low temperature. High charge mobility and diffusion length are maintained at high temperature beyond the tetragonal-to-cubic phase transition at ≈310 K.

778 citations


Journal ArticleDOI
TL;DR: In this article, uniform molybdenum disulfide (MoS2)/tungsten disulfides (WS2) quantum dots are synthesized by the combination of sonication and solvothermal treatment of bulk MoS2/WS2 at a mild temperature.
Abstract: In this work, uniform molybdenum disulfide (MoS2)/tungsten disulfide (WS2) quantum dots are synthesized by the combination of sonication and solvothermal treatment of bulk MoS2/WS2 at a mild temperature. The resulting products possess monolayer thickness with an average size about 3 nm. The highly exfoliated and defect-rich structure renders these quantum dots plentiful active sites for the catalysis of hydrogen evolution reaction (HER). The MoS2 quantum dots exhibit a small HER overpotential of ≈120 mV and long-term durability. Moreover, the strong fluorescence, good cell permeability, and low cytotoxicity make them promising and biocompatible probes for in vitro imaging. In addition, this work may provide an alternative facile approach to synthesize the quantum dots of transition metal dichalcogenides or other layered materials on a large scale.

714 citations


Journal ArticleDOI
TL;DR: In this paper, the state-of-the-art progress of semiconductor/semiconductor heterostructured photocatalysts with diverse models, including type-I and type-II heterojunctions, Z-scheme system, p-n heterojunction, and homojunction band alignments, were explored for effective improvement of photocatalysis activity through increase of the visible-light absorption, promotion of separation, and transportation of the photoinduced charge carries.
Abstract: Semiconductor photocatalysts have received much attention in recent years due to their great potentials for the development of renewable energy technologies, as well as for environmental protection and remediation. The effective harvesting of solar energy and suppression of charge carrier recombination are two key aspects in photocatalysis. The formation of heterostructured photocatalysts is a promising strategy to improve photocatalytic activity, which is superior to that of their single component photocatalysts. This Feature Article concisely summarizes and highlights the state-of-the-art progress of semiconductor/semiconductor heterostructured photocatalysts with diverse models, including type-I and type-II heterojunctions, Z-scheme system, p–n heterojunctions, and homojunction band alignments, which were explored for effective improvement of photocatalytic activity through increase of the visible-light absorption, promotion of separation, and transportation of the photoinduced charge carries, and enhancement of the photocatalytic stability.

680 citations


Journal ArticleDOI
TL;DR: In this article, a novel hybrid electrocatalyst consisting of nitrogen-doped graphene/cobalt-embedded porous carbon polyhedron was prepared through simple pyrolysis of graphene oxide-supported cobalt-based zeolitic imidazolate-frameworks.
Abstract: A novel hybrid electrocatalyst consisting of nitrogen-doped graphene/cobalt-embedded porous carbon polyhedron (N/Co-doped PCP//NRGO) is prepared through simple pyrolysis of graphene oxide-supported cobalt-based zeolitic imidazolate-frameworks. Remarkable features of the porous carbon structure, N/Co-doping effect, introduction of NRGO, and good contact between N/Co-doped PCP and NRGO result in a high catalytic efficiency. The hybrid shows excellent electrocatalytic activities and kinetics for oxygen reduction reaction in basic media, which compares favorably with those of the Pt/C catalyst, together with superior durability, a four-electron pathway, and excellent methanol tolerance. The hybrid also exhibits superior performance for hydrogen evolution reaction, offering a low onset overpotential of 58 mV and a stable current density of 10 mA cm−2 at 229 mV in acid media, as well as good catalytic performance for oxygen evolution reaction (a small overpotential of 1.66 V for 10 mA cm−2 current density). The dual-active-site mechanism originating from synergic effects between N/Co-doped PCP and NRGO is responsible for the excellent performance of the hybrid. This development offers an attractive catalyst material for large-scale fuel cells and water splitting technologies.

673 citations


Journal ArticleDOI
TL;DR: In this article, the growth of CoP mesoporosity nanorod arrays on conductive Ni foam through an electrodeposition strategy is reported, which can be directly employed as a bifunctional and flexible working electrode for both hydrogen and oxygen evolution reactions, showing superior activities as compared with noble metal benchmarks and state-of-theart transition-metal-based catalysts.
Abstract: Water splitting for the production of hydrogen and oxygen is an appealing solution to advance many sustainable and renewable energy conversion and storage systems, while the key fact depends on the innovative exploration regarding the design of efficient electrocatalysts. Reported herein is the growth of CoP mesoporous nanorod arrays on conductive Ni foam through an electrodeposition strategy. The resulting material of well-defined mesoporosity and a high specific surface area (148 m2 g−1) can be directly employed as a bifunctional and flexible working electrode for both hydrogen and oxygen evolution reactions, showing superior activities as compared with noble metal benchmarks and state-of-the-art transition-metal-based catalysts. This is intimately related to the unique nanorod array electrode configuration, leading to excellent electric interconnection and improved mass transport. A further step is taken toward an alkaline electrolyzer that can achieve a current density of 10 mA cm−2 at a voltage around 1.62 V over a long-term operation, better than the combination of Pt and IrO2. This development is suggested to be readily extended to obtain other electrocatalysis systems for scale-up water-splitting technology.

666 citations


Journal ArticleDOI
TL;DR: In this paper, a kinetic study on model compounds reveals the occurrence of transamination of vinylogous urethanes in a good temperature window without side reactions without making use of any catalyst, and the vitrimer nature of these networks is examined by solubility, stress-relaxation, and creep experiments.
Abstract: Vitrimers are a new class of polymeric materials with very attractive properties, since they can be reworked to any shape while being at the same time permanently cross-linked. As an alternative to the use of transesterification chemistry, we explore catalyst-free transamination of vinylogous urethanes as an exchange reaction for vitrimers. First, a kinetic study on model compounds reveals the occurrence of transamination of vinylogous urethanes in a good temperature window without side reactions. Next, poly(vinylogous urethane) networks with a storage modulus of approximate to 2.4 GPa and a glass transition temperature above 80 degrees C are prepared by bulk polymerization of cyclohexane dimethanol bisacetoacetate, m-xylylene diamine, and tris(2-aminoethyl) amine. The vitrimer nature of these networks is examined by solubility, stress-relaxation, and creep experiments. Relaxation times as short as 85 s at 170 degrees C are observed without making use of any catalyst. In addition, the networks are recyclable up to four times by consecutive grinding/compression molding cycles without signifi cant mechanical or chemical degradation.

642 citations


Journal ArticleDOI
TL;DR: In this paper, a facile one-pot hydrothermal method was used to construct a two-dimensional heterointerface for layered metal sulfides/graphene composites as high-performance electrode materials for sodium-ion batteries.
Abstract: Graphene has been widely used as conformal nanobuilding blocks to improve the electrochemical performance of layered metal sulfides (MoS2, WS2, SnS, and SnS2) as anode materials for sodium-ion batteries. However, it still lacks in-depth understanding of the synergistic effect between these layered sulfides and graphene, which contributes to the enhanced electroactivity for sodium-ion batteries. Here, MoS2/reduced graphene oxide (RGO) nanocomposites with intimate two-dimensional heterointerfaces are prepared by a facile one-pot hydrothermal method. The heterointerfacial area can be effectively tuned by changing the ratio of MoS2 to RGO. When used as anode materials for sodium-ion batteries, the synergistic effect contributing to the enhanced reversible capacity of MoS2/RGO nanocomposites is closely related with the heterointerfacial area. The computational results demonstrate that Na prefers to be adsorbed on MoS2 in the MoS2/RGO heterostructure rather than intercalate into the MoS2/RGO heterointerface. Interestingly, the MoS2/RGO heterointerfaces can significantly increase the electronic conductivity of MoS2, store more Na ions, while maintaining the high diffusion mobility of Na atoms on MoS2 surface and high electron transfer efficiency from Na to MoS2. It is expected that the efforts to establish the correlation between the two-dimensional heterointerface and the electrochemical sodium-ion storage performance offer fundamental understanding for the rational design of layered metal sulfides/graphene composites as high-performance electrode materials for sodium-ion batteries.

Journal ArticleDOI
TL;DR: In this article, natural graphite is used as an anode material for Na ion batteries and shown to have a reversible capacity of ≈150 mAh g−1 with a cycle stability for 2500 cycles.
Abstract: This work reports that natural graphite is capable of Na insertion and extraction with a remarkable reversibility using ether-based electrolytes. Natural graphite (the most well-known anode material for Li–ion batteries) has been barely studied as a suitable anode for Na rechargeable batteries due to the lack of Na intercalation capability. Herein, graphite is not only capable of Na intercalation but also exhibits outstanding performance as an anode for Na ion batteries. The graphite anode delivers a reversible capacity of ≈150 mAh g−1 with a cycle stability for 2500 cycles, and more than 75 mAh g−1 at 10 A g−1 despite its micrometer-size (≈100 μm). An Na storage mechanism in graphite, where Na+-solvent co-intercalation occurs combined with partial pseudocapacitive behaviors, is revealed in detail. It is demonstrated that the electrolyte solvent species significantly affect the electrochemical properties, not only rate capability but also redox potential. The feasibility of graphite in a Na full cell is also confirmed in conjunction with the Na1.5VPO4.8F0.7 cathode, delivering an energy of ≈120 Wh kg−1 while maintaining ≈70% of the initial capacity after 250 cycles. This exceptional behavior of natural graphite promises new avenues for the development of cost-effective and reliable Na ion batteries.

Journal ArticleDOI
TL;DR: In this paper, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS).
Abstract: Stretchable electronics have recently been extensively investigated for the development of highly advanced human-interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching-releasing cycles. When the sensor is attached to the human body, it functions as a health-monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ-LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.

Journal ArticleDOI
TL;DR: In this paper, a self-driven MoS2/Si heterojunction photodetector is proposed, which is sensitive to a broadband wavelength from visible light to near-infrared light, showing an extremely high detectivity up to ≈1013 Jones (Jones = cm Hz 1/2 W−1), and ultrafast response speed of ≈3 μs.
Abstract: As an interesting layered material, molybdenum disulfide (MoS2) has been extensively studied in recent years due to its exciting properties. However, the applications of MoS2 in optoelectronic devices are impeded by the lack of high-quality p–n junction, low light absorption for mono-/multilayers, and the difficulty for large-scale monolayer growth. Here, it is demonstrated that MoS2 films with vertically standing layered structure can be deposited on silicon substrate with a scalable sputtering method, forming the heterojunction-type photodetectors. Molecular layers of the MoS2 films are perpendicular to the substrate, offering high-speed paths for the separation and transportation of photo-generated carriers. Owing to the strong light absorption of the relatively thick MoS2 film and the unique vertically standing layered structure, MoS2/Si heterojunction photodetectors with unprecedented performance are actualized. The self-driven MoS2/Si heterojunction photodetector is sensitive to a broadband wavelength from visible light to near-infrared light, showing an extremely high detectivity up to ≈1013 Jones (Jones = cm Hz1/2 W−1), and an ultrafast response speed of ≈3 μs. The performance is significantly better than the photodetectors based on mono-/multilayer MoS2 nanosheets. Additionally, the MoS2/Si photodetectors exhibit excellent stability in air for a month. This work unveils the great potential of MoS2/Si heterojunction for optoelectronic applications.

Journal ArticleDOI
Yongchang Liu1, Ning Zhang1, Lifang Jiao1, Zhanliang Tao1, Jun Chen1 
TL;DR: In this article, ultrasmall Sn nanoparticles (≈8 nm) homogeneously embedded in spherical carbon network (denoted as 8-Sn@C) is prepared using an aerosol spray pyrolysis method.
Abstract: Designed as a high-capacity, high-rate, and long-cycle life anode for sodium-ion batteries, ultrasmall Sn nanoparticles (≈8 nm) homogeneously embedded in spherical carbon network (denoted as 8-Sn@C) is prepared using an aerosol spray pyrolysis method. Instrumental analyses show that 8-Sn@C nanocomposite with 46 wt% Sn and a BET surface area of 150.43 m2 g−1 delivers an initial reversible capacity of ≈493.6 mA h g−1 at the current density of 200 mA g−1, a high-rate capacity of 349 mA h g−1 even at 4000 mA g−1, and a stable capacity of ≈415 mA h g−1 after 500 cycles at 1000 mA g−1. The remarkable electrochemical performance of 8-Sn@C is owing to the synergetic effects between the well-dispersed ultrasmall Sn nanoparticles and the conductive carbon network. This unique structure of very-fine Sn nanoparticles embedded in the porous carbon network can effectively suppress the volume fluctuation and particle aggregation of tin during prolonged sodiation/desodiation process, thus solving the major problems of pulverization, loss of electrical contact and low utilization rate facing Sn anode.

Journal ArticleDOI
TL;DR: The developed hydrogel shows excellent self‐healing ability under physiological conditions with a high healing efficiency without need for any external stimuli and holds great potential for applications in various biomedical fields, e.g., as cell or drug delivery carriers.
Abstract: A novel biocompatible polysaccharide-based self-healing hydrogel, CEC-l-OSA-l-ADH hydrogel (“l” means “linked-by”), is developed by exploiting the dynamic reaction of N-carboxyethyl chitosan (CEC) and adipic acid dihydrazide (ADH) with oxidized sodium alginate (OSA). The self-healing ability, as demonstrated by rheological recovery, macroscopic observation, and beam-shaped strain compression measurement, is attributed to the coexistence of dynamic imine and acylhydrazone bonds in the hydrogel networks. The CEC-l-OSA-l-ADH hydrogel shows excellent self-healing ability under physiological conditions with a high healing efficiency (up to 95%) without need for any external stimuli. In addition, the CEC-l-OSA-l-ADH hydrogel exhibits good cytocompatibility and cell release as demonstrated by three-dimensional cell encapsulation. With these superior properties, the developed hydrogel holds great potential for applications in various biomedical fields, e.g., as cell or drug delivery carriers.

Journal ArticleDOI
Qiang Chen, Lin Zhu, Hong Chen1, Hongli Yan, Lina Huang, Jia Yang, Jie Zheng1 
TL;DR: In this paper, a new design strategy is proposed and demonstrated to improve both fatigue resistance and self-healing property of double network (DN) gels by introducing a ductile, nonsoft gel with strong hydrophobic interactions as the second network.
Abstract: Double network (DN) hydrogels with two strong asymmetric networks being chemically linked have demonstrated their excellent mechanical properties as the toughest hydrogels, but chemically linked DN gels often exhibit negligible fatigue resistance and poor self-healing property due to the irreversible chain breaks in covalent-linked networks. Here, a new design strategy is proposed and demonstrated to improve both fatigue resistance and self-healing property of DN gels by introducing a ductile, nonsoft gel with strong hydrophobic interactions as the second network. Based on this design strategy, a new type of fully physically cross-linked Agar/hydrophobically associated polyacrylamide (HPAAm) DN gels are synthesized by a simple one-pot method. Agar/HPAAm DN gels exhibit excellent mechanical strength and high toughness, comparable to the reported DN gels. More importantly, because the ductile and tough second network of HPAAm can bear stress and reconstruct network structure, Agar/HPAAm DN gels also demonstrate rapid self-recovery, remarkable fatigue resistance, and notable self-healing property without any external stimuli at room temperature. In contrast to the former DN gels in both network structures and underlying association forces, this new design strategy to prepare highly mechanical DN gels provides a new avenue to better understand the fundamental structure-property relationship of DN hydrogels, thus broadening current hydrogel research and applications.

Journal ArticleDOI
TL;DR: In this article, an AgNW-embedded styrene-butadiene-styrene (SBS) elastomeric matrix is fabricated by a simple wet spinning method.
Abstract: Stretchable conductive fi bers have received signifi cant attention due to their possibility of being utilized in wearable and foldable electronics. Here, highly stretchable conductive fi ber composed of silver nanowires (AgNWs) and silver nanoparticles (AgNPs) embedded in a styrene‐butadiene‐styrene (SBS) elastomeric matrix is fabricated. An AgNW-embedded SBS fi ber is fabricated by a simple wet spinning method. Then, the AgNPs are formed on both the surface and inner region of the AgNW-embedded fi ber via repeated cycles of silver precursor absorption and reduction processes. The AgNW-embedded conductive fi ber exhibits superior initial electrical conductivity ( σ 0 = 2450 S cm −1 ) and elongation at break (900% strain) due to the high weight percentage of the conductive fi llers and the use of a highly stretchable SBS elastomer matrix. During the stretching, the embedded AgNWs act as conducting bridges between AgNPs, resulting in the preservation of electrical conductivity under high strain (the rate of conductivity degradation, σ / σ 0 = 4.4% at 100% strain). The AgNW-embedded conductive fi bers show the strain-sensing behavior with a broad range of applied tensile strain. The AgNW reinforced highly stretchable conductive fi bers can be embedded into a smart glove for detecting sign language by integrating fi ve composite fi bers in the glove, which can successfully perceive human motions.

Journal ArticleDOI
TL;DR: In this paper, a novel anode material for sodium-ion batteries consisting of 3D graphene microspheres divided into several tens of uniform nanospheres coated with few-layered MoS2 by a one-pot spray pyrolysis process is prepared.
Abstract: A novel anode material for sodium-ion batteries consisting of 3D graphene microspheres divided into several tens of uniform nanospheres coated with few-layered MoS2 by a one-pot spray pyrolysis process is prepared. The first discharge/charge capacities of the composite microspheres are 797 and 573 mA h g−1 at a current density of 0.2 A g−1. The 600th discharge capacity of the composite microspheres at a current density of 1.5 A g−1 is 322 mA h g−1. The Coulombic efficiency during the 600 cycles is as high as 99.98%. The outstanding Na ion storage properties of the 3D MoS2–graphene composite microspheres may be attributed to the reduced stacking of the MoS2 layers and to the 3D structure of the porous graphene microspheres. The reduced stacking of the MoS2 layers relaxes the strain and lowers the barrier for Na+ insertion. The empty nanospheres of the graphene offer voids for volume expansion and pathways for fast electron transfer during repeated cycling.

Journal ArticleDOI
TL;DR: In this paper, a new class of multifunctional electrocatalysts consisting of dominant metallic Ni or Co with small fraction of their oxides anchored onto nitrogen-doped reduced graphene oxide (rGO) including Co-CoO/N-rGO and Ni-NiO/Ni-N-RGO were prepared via a pyrolysis of graphene oxide and cobalt or nickel salts.
Abstract: Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) along with hydrogen evolution reaction (HER) have been considered critical processes for electrochemical energy conversion and storage through metal-air battery, fuel cell, and water electrolyzer technologies. Here, a new class of multifunctional electrocatalysts consisting of dominant metallic Ni or Co with small fraction of their oxides anchored onto nitrogen-doped reduced graphene oxide (rGO) including Co-CoO/N-rGO and Ni-NiO/N-rGO are prepared via a pyrolysis of graphene oxide and cobalt or nickel salts. Ni-NiO/N-rGO shows the higher electrocatalytic activity for the OER in 0.1 m KOH with a low overpotential of 0.24 V at a current density of 10 mA cm−2, which is superior to that of the commercial IrO2. In addition, it exhibits remarkable activity for the HER, demonstrating a low overpotential of 0.16 V at a current density of 20 mA cm−2 in 1.0 m KOH. Apart from similar HER activity to the Ni-based catalyst, Co-CoO/N-rGO displays the higher activity for the ORR, comparable to Pt/C in zinc-air batteries. This work provides a new avenue for the development of multifunctional electrocatalysts with optimal catalytic activity by varying transition metals (Ni or Co) for these highly demanded electrochemical energy technologies.

Journal ArticleDOI
TL;DR: The fabrication of a transparent and stretchable iHMI system composed of wearable mechanical sensors and stimulators is reported and the control of a robot arm for various motions and the feedback stimulation upon successful executions of commands are demonstrated using the wearable iH MI system.
Abstract: An interactive human-machine interface (iHMI) enables humans to control hardware and collect feedback information. In particular, wearable iHMI systems have attracted tremendous attention owing to their potential for use in personal mobile electronics and the Internet of Things. Although significant progress has been made in the development of iHMI systems, those based on rigid electronics have constraints in terms of wearability, comfortability, signal-to-noise ratio (SNR), and aesthetics. Herein the fabrication of a transparent and stretchable iHMI system composed of wearable mechanical sensors and stimulators is reported. The ultrathin and lightweight design of the system allows superior wearability and high SNR. The use of conductive/piezoelectric graphene heterostructures, which consist of poly(l-lactic acid), single-walled carbon nanotubes, and silver nanowires, results in high transparency, excellent performance, and low power consumption as well as mechanical deformability. The control of a robot arm for various motions and the feedback stimulation upon successful executions of commands are demonstrated using the wearable iHMI system.

Journal ArticleDOI
TL;DR: In this article, the in-plane and cross-plane thermal conductivity of reduced graphene oxide films subjected to a high-temperature treatment of up to 1000 °C was investigated.
Abstract: Thermal conductivity of free-standing reduced graphene oxide films subjected to a high-temperature treatment of up to 1000 °C is investigated. It is found that the high-temperature annealing dramatically increases the in-plane thermal conductivity, K, of the films from ≈3 to ≈61 W m−1 K−1 at room temperature. The cross-plane thermal conductivity, K⊥, reveals an interesting opposite trend of decreasing to a very small value of ≈0.09 W m−1 K−1 in the reduced graphene oxide films annealed at 1000 °C. The obtained films demonstrate an exceptionally strong anisotropy of the thermal conductivity, K/K⊥ ≈ 675, which is substantially larger even than in the high-quality graphite. The electrical resistivity of the annealed films reduces to 1–19 Ω □−1. The observed modifications of the in-plane and cross-plane thermal conductivity components resulting in an unusual K/K⊥ anisotropy are explained theoretically. The theoretical analysis suggests that K can reach as high as ≈500 W m−1 K−1 with the increase in the sp2 domain size and further reduction of the oxygen content. The strongly anisotropic heat conduction properties of these films can be useful for applications in thermal management.

Journal ArticleDOI
TL;DR: In this paper, a carbon shell-protection solution was proposed and a ferroferric oxide-carbon (Fe3O4-C) binder-free nanorod array anode exhibiting much improved cyclic stability (from only hundreds of times to >5000 times), excellent rate performance, and a high capacity of ≈7776.36 C cm−3 (≈0.4278 C cm −2; 247.5 mAh g−1, 71.4% of the theoretical value) in alkaline electrolyte.
Abstract: Iron oxides are promising to be utilized in rechargeable alkaline battery with high capacity upon complete redox reaction (Fe3+ Fe0). However, their practical application has been hampered by the poor structural stability during cycling, presenting a challenge that is particularly huge when binder-free electrode is employed. This paper proposes a “carbon shell-protection” solution and reports on a ferroferric oxide–carbon (Fe3O4–C) binder-free nanorod array anode exhibiting much improved cyclic stability (from only hundreds of times to >5000 times), excellent rate performance, and a high capacity of ≈7776.36 C cm−3 (≈0.4278 C cm−2; 247.5 mAh g−1, 71.4% of the theoretical value) in alkaline electrolyte. Furthermore, by pairing with a capacitive carbon nanotubes (CNTs) film cathode, a unique flexible solid-state rechargeable alkaline battery-supercapacitor hybrid device (≈360 μm thickness) is assembled. It delivers high energy and power densities (1.56 mWh cm−3; 0.48 W cm−3/≈4.8 s charging), surpassing many recently reported flexible supercapacitors. The highest energy density value even approaches that of Li thin-film batteries and is about several times that of the commercial 5.5 V/100 mF supercapacitor. In particular, the hybrid device still maintains good electrochemical attributes in cases of substantially bending, high mechanical pressure, and elevated temperature (up to 80 °C), demonstrating high environmental suitability.

Journal ArticleDOI
TL;DR: In this paper, a low-cost fabrication strategy to efficiently construct highly sensitive graphite-based strain sensors by pencil-trace drawn on flexible printing papers is reported, which can be operated at only two batteries voltage of 3 V, and can be applied to variously monitoring microstructural changes and human motions with fast response/relaxation times of 110 ms, a high gauge factor (GF) of 536.6, and high stability >10 000 bending-unbending cycles.
Abstract: Functional electrical devices have promising potentials in structural health monitoring system, human-friendly wearable interactive system, smart robotics, and even future multifunctional intelligent room. Here, a low-cost fabrication strategy to efficiently construct highly sensitive graphite-based strain sensors by pencil-trace drawn on flexible printing papers is reported. The strain sensors can be operated at only two batteries voltage of 3 V, and can be applied to variously monitoring microstructural changes and human motions with fast response/relaxation times of 110 ms, a high gauge factor (GF) of 536.6, and high stability >10 000 bending–unbending cycles. Through investigation of service behaviors of the sensors, it is found that the microcracks occur on the surface of the pencil-trace and have a major influence on the functions of the strain sensors. These performances of the strain sensor attain and even surpass the properties of recent strain sensing devices with subtle design of materials and device architectures. The pen-on-paper (PoP) approach may further develop portable, environmentally friendly, and economical lab-on-paper applications and offer a valuable method to fabricate other multifunctional devices.

Journal ArticleDOI
TL;DR: In this paper, a liquid-metal-based triboelectric nanogenerator (LM-TENG) is developed for high power generation through conversion of mechanical energy, which allows a total contact between the metal and the dielectric.
Abstract: Harvesting ambient mechanical energy is a key technology for realizing self-powered electronics, which has tremendous applications in wireless sensing networks, implantable devices, portable electronics, etc. The currently reported triboelectric nanogenerator (TENG) mainly uses solid materials, so that the contact between the two layers cannot be 100% with considering the roughness of the surfaces, which greatly reduces the total charge density that can be transferred and thus the total energy conversion efficiency. In this work, a liquid-metal-based triboelectric nanogenerator (LM-TENG) is developed for high power generation through conversion of mechanical energy, which allows a total contact between the metal and the dielectric. Due to that the liquid–solid contact induces large contacting surface and its shape adaptive with the polymer thin films, the LM-TENG exhibits a high output charge density of 430 μC m−2, which is four to five times of that using a solid thin film electrode. And its power density reaches 6.7 W m−2 and 133 kW m−3. More importantly, the instantaneous energy conversion efficiency is demonstrated to be as high as 70.6%. This provides a new approach for improving the performance of the TENG for special applications. Furthermore, the liquid easily fluctuates, which makes the LM-TENG inherently suitable for vibration energy harvesting.

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TL;DR: In this paper, a composite material with well dispersed Fe2O3 quantum dots (QDs, ≈2 nm) decorated on functionalized graphene-sheets (FGS) is prepared by a facile and scalable method.
Abstract: For building high-energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe2O3 has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe2O3-based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe2O3 quantum dots (QDs, ≈2 nm) decorated on functionalized graphene-sheets (FGS) is prepared by a facile and scalable method. The Fe2O3 QDs/FGS composites exhibit a large specific capacitance up to 347 F g−1 in 1 m Na2SO4 between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe2O3/FGS as anode and MnO2/FGS as cathode in 1 m Na2SO4 aqueous electrolyte. The Fe2O3/FGS//MnO2/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg−1 at a power density of 100 W kg−1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe2O3 QDs/FGS composites make them promising as anode materials for high-performance asymmetric supercapacitors.

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TL;DR: In this article, the UiO-66/carbon nitride nanosheet heterogeneous photocatalyst exhibits a much higher photocatalytic activity for the CO2 conversion than that of bare carbon nitride nano-heets.
Abstract: UiO-66, a zirconium based metal–organic framework, is incorporated with nanosized carbon nitride nanosheets via a facile electrostatic self-assembly method. This hybrid structure exhibits a large surface area and strong CO2 capture ability due to the introduction of UiO-66. We demonstrate that electrons from the photoexcited carbon nitride nanosheet can transfer to UiO-66, which can substantially suppress electron–hole pair recombination in the carbon nitride nanosheet, as well as supply long-lived electrons for the reduction of CO2 molecules that are adsorbed in UiO-66. As a result, the UiO-66/carbon nitride nanosheet heterogeneous photocatalyst exhibits a much higher photocatalytic activity for the CO2 conversion than that of bare carbon nitride nanosheets. We believe this self-assembly method can be extended to other carbon nitride nanosheet loaded materials.

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TL;DR: In this paper, a novel hybrid anode is synthesized consisting of ultrafine, few-layered SnS2 anchored on few-layer reduced graphene oxide (rGO) by a facile solvothermal route.
Abstract: Na-ion Batteries have been considered as promising alternatives to Li-ion batteries due to the natural abundance of sodium resources. Searching for high-performance anode materials currently becomes a hot topic and also a great challenge for developing Na-ion batteries. In this work, a novel hybrid anode is synthesized consisting of ultrafine, few-layered SnS2 anchored on few-layered reduced graphene oxide (rGO) by a facile solvothermal route. The SnS2/rGO hybrid exhibits a high capacity, ultralong cycle life, and superior rate capability. The hybrid can deliver a high charge capacity of 649 mAh g−1 at 100 mA g−1. At 800 mA g−1 (1.8 C), it can yield an initial charge capacity of 469 mAh g−1, which can be maintained at 89% and 61%, respectively, after 400 and 1000 cycles. The hybrid can also sustain a current density up to 12.8 A g−1 (≈28 C) where the charge process can be completed in only 1.3 min while still delivering a charge capacity of 337 mAh g−1. The fast and stable Na-storage ability of SnS2/rGO makes it a promising anode for Na-ion batteries.

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TL;DR: In this paper, a simple low-temperature synthesis approach is reported for planting CdS-sensitized 1D ZnO nanorod arrays on the 2D graphene (GR) sheet to obtain the ternary hierarchical nanostructures.
Abstract: A simple, low-temperature synthesis approach is reported for planting CdS-sensitized 1D ZnO nanorod arrays on the 2D graphene (GR) sheet to obtain the ternary hierarchical nanostructures, during which graphene oxide (GO) as the precursor of GR acts as a flexible substrate for the formation of ZnO nanorod arrays. The hierarchical CdS-1D ZnO-2D GR hybrids can serve as an efficient visible-light-driven photocatalyst for selective organic transformations. The fast electron transport of 1D ZnO nanorods, the well-known electronic conductivity of 2D GR, the intense visible-light absorption of CdS, the unique hierarchical structure, and the matched energy levels of CdS, ZnO and GR efficiently boost the photogenerated charge carriers separation and transfer across the interfacial domain of hierarchical CdS-1D ZnO-2D GR hybrids under visible light irradiation via three-level electron transfer process. Furthermore, the superior reusability of ternary hybrids is achieved by controlling the reaction parameters, i.e., using visible light irradiation and holes scavenger to prevent ZnO and CdS from photocorrosion. This work demonstrates a facile way of fabricating hierarchical CdS-1D ZnO-2D GR hybrids in a controlled manner and highlights a promising scope of adopting integrative photosensitization and co-catalyst strategy to design more efficient semiconductor-based composite photocatalysts toward solar energy capture and conversion.

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Rutao Wang1, Junwei Lang1, Peng Zhang1, Zongyuan Lin1, Xingbin Yan1 
TL;DR: Li-ion hybrid capacitors (LIHCs) are attracting significant attention due to the good combination with the advantages of conventional Li-ion batteries and supercapacitors as discussed by the authors.
Abstract: Li-ion hybrid capacitors (LIHCs), consisting of an energy-type redox anode and a power-type double-layer cathode, are attracting significant attention due to the good combination with the advantages of conventional Li-ion batteries and supercapacitors. However, most anodes are battery-like materials with the sluggish kinetics of Li-ion storage, which seriously restrict the energy storage of LIHCs at the high charge/discharge rates. Herein, vanadium nitride (VN) nanowire is demonstated to have obvious pseudocapacitive characteristic of Li-ion storage and can get further gains in energy storage through a 3D porous architecture with the assistance of conductive reduced graphene oxide (RGO). The as-prepared 3D VN–RGO composite exhibits the large Li-ion storage capacity and fast charge/discharge rate within a wide working widow from 0.01–3 V (vs Li/Li + ), which could potentially boost the operating potential and the energy and power densities of LIHCs. By employing such 3D VN–RGO composite and porous carbon nanorods with a high surface area of 3343 m 2 g −1 as the anode and cathode, respectively, a novel LIHCs is fabricated with an ultrahigh energy density of 162 Wh kg −1 at 200 W kg −1 , which also remains 64 Wh kg −1 even at a high power density of 10 kW kg −1 .