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3D Graphene Networks Encapsulated with Ultrathin SnS [email protected] Mesoporous Carbon Spheres Nanocomposite with Pseudocapacitance‐Enhanced Lithium and Sodium Storage Kinetics

2019-03-12T10:34:52+00:00March 12th, 2019|Categories: Publications|Tags: , |

A 3D honeycomb‐like network architecture, in which SnS nanosheets are first located both inside and outside hollow mesoporous carbon spheres and further homogeneously encapsulated in the reduced graphene oxide, is prepared and shows pseudocapacitance‐enhanced lithium and sodium storage kinetics. Abstract The lithium and sodium storage performances of SnS anode often undergo rapid capacity decay and poor rate capability owing to its huge volume fluctuation and structural instability upon the repeated charge/discharge processes. Herein, a novel and versatile method is described for in situ synthesis of ultrathin SnS nanosheets inside and outside hollow mesoporous carbon spheres crosslinked reduced graphene oxide networks. Thus, 3D honeycomb‐like network architecture is formed. Systematic electrochemical studies manifest that this nanocomposite as anode material for lithium‐ion batteries delivers a high charge capacity of 1027 mAh g−1 at 0.2 A g−1 after 100 cycles. Meanwhile, the as‐developed nanocomposite still retains a charge capacity of 524 mAh g−1 at 0.1 A g−1 after 100 cycles for sodium‐ion batteries. In addition, the electrochemical kinetics analysis verifies the basic principles of enhanced rate capacity. The appealing electrochemical performance for both lithium‐ion batteries and sodium‐ion batteries can be mainly related to the porous 3D interconnected architecture, in which the nanoscale SnS nanosheets not only offer decreased ion diffusion pathways and fast Li+/Na+ transport kinetics, but also the 3D interconnected conductive networks constructed from the hollow mesoporous carbon spheres and reduced graphene oxide enhance the conductivity and ensure the structural integrity.

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Hexagonal Boron Nitride Growth on Cu‐Si Alloy: Morphologies and Large Domains

2019-03-12T10:34:49+00:00March 12th, 2019|Categories: Publications|Tags: , , |

Large domains of hexagonal boron nitride (h‐BN) are deposited on silicon‐doped Cu substrate. A rich variety of h‐BN domain morphologies can be delicately controlled through the growth temperature, from fractal tree patterns to dendritic triangles. Abstract Controllable synthesis of high‐quality hexagonal boron nitride (h‐BN) is desired toward the industrial application of 2D devices based on van der Waals heterostructures. Substantial efforts are devoted to synthesize h‐BN on copper through chemical vapor deposition, which has been successfully applied to grow graphene. However, the progress in synthesizing h‐BN has been significantly retarded, and it is still challenging to realize millimeter‐scale domains and control their morphologies reliably. Here, the nucleation density of h‐BN on Cu is successfully reduced by over two orders of magnitude by simply introducing a small amount of silicon, giving rise to large triangular domains with maximum 0.25 mm lateral size. Moreover, the domain morphologies can be modified from needles, tree patterns, and leaf darts to triangles through controlling the growth temperature. The presence of silicon alters the growth mechanism from attachment‐limited mode to diffusion‐limited mode, leading to dendrite domains that are rarely observed on pure Cu. A phase‐field model is utilized to reveal the growing dynamics regarding B‐N diffusion, desorption, flux, and reactivity variables, and explain the morphology evolution. The work sheds lights on the h‐BN growth toward large single crystals and morphology probabilities.

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Engineering 2D Metal–Organic Framework/MoS2 Interface for Enhanced Alkaline Hydrogen Evolution

2019-03-12T10:34:45+00:00March 12th, 2019|Categories: Publications|Tags: |

2D Co‐BDC/MoS2 hybrid nanosheets are synthesized via a facile sonication‐assisted solution strategy. The introduction of Co‐BDC induces the partial phase transfer of MoS2 from semiconducting 2H‐phase to metallic 1T‐phase. The obtained Co‐BDC/MoS2 hybrid nanosheets demonstrate remarkable catalytic activity for alkaline hydrogen evolution due to the generated 1T‐phase MoS2 and well‐designed Co‐BDC/MoS2 interface. Abstract 2D metal–organic frameworks (MOFs) have been widely investigated for electrocatalysis because of their unique characteristics such as large specific surface area, tunable structures, and enhanced conductivity. However, most of the works are focused on oxygen evolution reaction. There are very limited numbers of reports on MOFs for hydrogen evolution reaction (HER), and generally these reported MOFs suffer from unsatisfactory HER activities. In this contribution, novel 2D Co‐BDC/MoS2 (BDC stands for 1,4‐benzenedicarboxylate, C8H4O4) hybrid nanosheets are synthesized via a facile sonication‐assisted solution strategy. The introduction of Co‐BDC induces a partial phase transfer from semiconducting 2H‐MoS2 to metallic 1T‐MoS2. Compared with 2H‐MoS2, 1T‐MoS2 can activate the inert basal plane to provide more catalytic active sites, which contributes significantly to improving HER activity. The well‐designed Co‐BDC/MoS2 interface is vital for alkaline HER, as Co‐BDC makes it possible to speed up the sluggish water dissociation (rate‐limiting step for alkaline HER), and modified MoS2 is favorable for the subsequent hydrogen generation step. As expected, the resultant 2D Co‐BDC/MoS2 hybrid nanosheets demonstrate remarkable catalytic activity and good stability toward alkaline HER, outperforming those of bare Co‐BDC, MoS2, and almost all the previously reported MOF‐based electrocatalysts.

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All‐Carbon Pressure Sensors with High Performance and Excellent Chemical Resistance

2019-03-12T10:34:43+00:00March 12th, 2019|Categories: Publications|Tags: , , |

An all‐carbon pressure sensor, with light weight (<10 mg), high performance, and high chemical stability, is designed by combining freestanding superelastic reduced graphene oxide (rGO) aerogel and highly conductive rGO paper. It displays application in monitoring real‐time human physiological signals and weighting droplets of commonly used liquid or even hazardous chemical reagents. Abstract An all‐carbon pressure sensor is designed and fabricated based on reduced graphene oxide (rGO) nanomaterials. By sandwiching one layer of superelastic rGO aerogel between two freestanding high‐conductive rGO thin papers, the sensor works based on the contact resistance at the aerogel–paper interfaces, getting rid of the alien materials such as polymers and metals adopted in traditional sensors. Without the limitation of alien materials, the all‐carbon sensors demonstrate an ultrawide detecting range (0.72 Pa–130 kPa), low energy consumption (≈0.58 µW), ultrahigh sensitivity (349–253 kPa−1) at low‐pressure regime (<1.4 Pa), fast response time (8 ms at 1 kPa), high stability (10 000 unloading–loading cycles between 0 and 1 kPa), light weight (<10 mg), easily scalable fabrication process, and excellent chemical stability. These merits enable them to detect real‐time human physiological signals and monitor the weights of various droplets of not only water but also hazardous chemical reagents including strong acid, strong alkali, and organic solvents. This shows their great potential applications in real‐time health monitoring, sport performance detecting, harsh environment‐related robotics and industry, and so forth.

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Silver‐Quantum‐Dot‐Modified MoO3 and MnO2 Paper‐Like Freestanding Films for Flexible Solid‐State Asymmetric Supercapacitors

2019-03-12T10:34:40+00:00March 12th, 2019|Categories: Publications|Tags: |

Highly conductive regions on the surfaces of MoO3 and MnO2 paper‐like freestanding films are formed with the addition of Ag quantum dots, which enhance the electrical conductivity of transition metal oxides and act to improve their pseudocapacitive storage properties. As a result, constructed flexible solid‐state asymmetric supercapacitors present outstanding electrochemical performances. Abstract Free‐standing paper‐like thin‐film electrodes have great potential to boost next‐generation power sources with highly flexible, ultrathin, and lightweight requirements. In this work, silver‐quantum‐dot‐ (2–5 nm) modified transition metal oxide (including MoO3 and MnO2) paper‐like electrodes are developed for energy storage applications. Benefitting from the ohmic contact at the interfaces between silver quantum dots and MoO3 nanobelts (or MnO2 nanowires) and the binder‐free nature and 0D/1D/2D nanostructured 3D network of the fabricated electrodes, substantial improvements on the electrical conductivity, efficient ionic diffusion, and areal capacitances of the hybrid nanostructure electrodes are observed. With this proposed strategy, the constructed asymmetric supercapacitors, with Ag quantum dots/MoO3 “paper” as anode, Ag quantum dots/MnO2 “paper” as cathode, and neutral Na2SO4/polyvinyl alcohol hydrogel as electrolyte, exhibit significantly enhanced energy and power densities in comparison with those of the supercapacitors without modification of Ag quantum dots on electrodes; present excellent cycling stability at different current densities and good flexibility under various bending states; offer possibilities as high‐performance power sources with low cost, high safety, and environmental friendly properties.

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Synthesis of Hydrogen‐Substituted Graphyne Film for Lithium–Sulfur Battery Applications

2019-03-12T10:34:38+00:00March 12th, 2019|Categories: Publications|Tags: |

A hydrogen‐substituted graphyne (HsGY) film is successfully synthesized on a gas/liquid interface using alkyne metathesis with 1,3,5‐tripynylbenzene (TPB) as the precursor. The synthesized HsGY film is used as a sulfur host matrix in lithium–sulfur batteries (LSBs) and presents high reversible capacity and stable cycle performance, which makes [email protected] a promising sulfur host material. Abstract Graphyne (GY) is a new type of carbon allotrope, which is viewed as a rapidly rising star in the carbon family referred to as 2D carbon allotropes due to its extraordinary properties. Considering the dynamic nature of the alkyne metathesis reaction, a hydrogen‐substituted graphyne (HsGY) film is successfully synthesized on a gas/liquid interface using 1,3,5‐tripynylbenzene (TPB) as the precursor. The synthesized HsGY film is used as a sulfur host matrix to be applied in lithium–sulfur batteries (LSBs). The [email protected] electrode is prepared using S8 as sulfur source and presents excellent electrochemical performance.

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Impact of Interfacial Electron Transfer on Electrochemical CO2 Reduction on Graphitic Carbon Nitride/Doped Graphene

2019-03-12T10:34:36+00:00March 12th, 2019|Categories: Publications|Tags: |

A series of graphitic carbon nitride/graphene (C3N4/XG) metal‐free catalysts are investigated for the electrochemical CO2 reduction reaction (CRR), demonstrating that a higher catalytic activity originates from more interfacial electron transfer. An overpotential of ‐0.28 V vs reverse hydrogen electrode shows the best CRR performance toward methane on C3N4/XG, which has not been achieved on any previously reported metallic CRR electrocatalysts. Abstract Effective electrocatalysts are required for the CO2 reduction reaction (CRR), while the factors that can impact their catalytic activity are yet to be discovered. In this article, graphitic carbon nitride (g‐C3N4) is used to investigate the feasibility of regulating its CRR catalytic performance by interfacial electron transfer. A series of g‐C3N4/graphene with and without heteroatom doping (C3N4/XG, XG = BG, NG, OG, PG, G) is comprehensively evaluated for CRR through computational methods. Variable adsorption energetics and electronic structures are observed among different doping cases, demonstrating that a higher catalytic activity originates from more interfacial electron transfer. An activity trend is obtained to show the best catalytic performance of CRR to methane on C3N4/XG with an overpotential of 0.45 V (i.e., −0.28 V vs reverse hydrogen electrode [RHE]). Such a low overpotential has never been achieved on any previously reported metallic CRR electrocatalysts, therefore indicating the availability of C3N4/XG for CO2 reduction and the applicability of electron transfer modulation to improve CRR catalytic performance.

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Discrimination of Protein Amino Acid or Its Protonated State at Single‐Residue Resolution by Graphene Nanopores

2019-03-12T10:34:34+00:00March 12th, 2019|Categories: Publications|Tags: |

A proof of principle study is performed to investigate the capability of protein sequencing by graphene nanopores integrated with atomic force microscopy using molecular dynamics simulations. The protein sequence and even its protonation state could be differentiated at single‐residue resolution by measuring dual‐mode signals including ionic current as well as pulling force using an integrated sensing system. Abstract The function of a protein is determined by the composition of amino acids and is essential to proteomics. However, protein sequencing remains challenging due to the protein’s irregular charge state and its high‐order structure. Here, a proof of principle study on the capability of protein sequencing by graphene nanopores integrated with atomic force microscopy is performed using molecular dynamics simulations. It is found that nanopores can discriminate a protein sequence and even its protonation state at single‐residue resolution. Both the pulling forces and current blockades induced by the permeation of protein residues are found to be highly correlated with the type of amino acids, which makes the residues identifiable. It is also found that aside from the dimension, both the conformation and charge state of the residue can significantly influence the force and current signal during its permeation through the nanopore. In particular, due to the electro‐osmotic flow effect, the blockade current for the double‐protonated histidine is slightly smaller than that for single‐protonated histidine, which makes it possible for discrimination of different protonation states of amino acids. The results reported here present a novel protein sequencing scheme using graphene nanopores combined with

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Glucose‐Induced Synthesis of 1T‐MoS2/C Hybrid for High‐Rate Lithium‐Ion Batteries

2019-03-12T10:34:32+00:00March 12th, 2019|Categories: Publications|Tags: |

1T‐MoS2 nanosheets covered by thin carbon layers possess several advantages. Expanded interlayer spacing can effectively release volume variation, high electrical conductivity can accelerate fast transfer of lithium ions and electrons, and the much smaller and fewer‐layer nanosheet structure can shorten the diffusion path of the lithium ions. Benefitting from the synergistic effect of these advantages, a 1T‐MoS2/C hybrid demonstrates excellent electrochemical performance. Abstract 1T phase MoS2 possesses higher conductivity than the 2H phase, which is a key parameter of electrochemical performance for lithium ion batteries (LIBs). Herein, a 1T‐MoS2/C hybrid is successfully synthesized through facile hydrothermal method with a proper glucose additive. The synthesized hybrid material is composed of smaller and fewer‐layer 1T‐MoS2 nanosheets covered by thin carbon layers with an enlarged interlayer spacing of 0.94 nm. When it is used as an anode material for LIBs, the enlarged interlayer spacing facilitates rapid intercalating and deintercalating of lithium ions and accommodates volume change during cycling. The high intrinsic conductivity of 1T‐MoS2 also contributes to a faster transfer of lithium ions and electrons. Moreover, much smaller and fewer‐layer nanosheets can shorten the diffusion path of lithium ions and accelerate reaction kinetics, leading to an improved electrochemical performance. It delivers a high initial capacity of 920.6 mAh g−1 at 1 A g−1 and the capacity can maintain 870 mAh g−1 even after 300 cycles, showing a superior cycling stability. The electrode presents a high rate performance as well with a reversible capacity of 600 mAh g−1 at 10 A g−1. These results

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Air‐Stable Polyphosphazene‐Functionalized Few‐Layer Black Phosphorene for Flame Retardancy of Epoxy Resins

2019-03-12T10:34:30+00:00March 12th, 2019|Categories: Publications|Tags: , |

Here, cross‐linked polyphosphazene‐functionalized black phosphorus (BP‐PZN) is developed with abundant –NH2 groups via a one‐pot polycondensation of 4,4′‐diaminodiphenyl ether and hexachlorocyclotriphosphazene on the surface of BP nanosheets. The resulting BP‐PZN is incorporated into epoxy resin (EP) to improve the flame‐retardant property and smoke suppression performance of EP nanocomposites. Abstract Similar to graphene, few‐layer black phosphorus (BP) features thermal stability, mechanical properties, and characteristic dimension effects, which has potential as a new member of nanofillers for fabricating polymer nanocomposites. Herein, a cross‐linked polyphosphazene‐functionalized BP (BP‐PZN) is developed with abundant –NH2 groups via a one‐pot polycondensation of 4,4′‐diaminodiphenyl ether and hexachlorocyclotriphosphazene on the surface of BP nanosheets. Whereafter, the resulting BP‐PZN is incorporated into epoxy resin (EP) to study the flame‐retardant property and smoke suppression performance. Cone results show that the introduction of 2 wt% BP‐PZN distinctly improves the flame‐retardant property of EP, for instance, 59.4% decrease in peak heat release rate and 63.6% reduction in total heat release. The diffusion of pyrolysis products from EP during combustion is obviously suppressed after incorporating the BP‐PZN nanosheets. Meanwhile, the EP/BP‐PZN nanocomposites exhibit air stability after exposure to ambient conditions for four months. The air stability of the BP nanosheets in EP matrix is assigned to surface wrapping by PZN and embedded in the polymer matrix as dual protection. As a new member of the 2D nanomaterials, BP nanosheets have potential to be a new choice for fabricating high‐performance nanocomposites.

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Few‐Layered Tin Sulfide Nanosheets Supported on Reduced Graphene Oxide as a High‐Performance Anode for Potassium‐Ion Batteries

2019-03-12T10:34:28+00:00March 12th, 2019|Categories: Publications|Tags: , , |

Few‐layered SnS2 nanosheets vertically alligned on reduced graphene oxide nanosheets are demonstrated as high‐performance anode material for potassium‐ion batteries. Besides the high specific capacities based on sequential conversion and alloying reactions, excellent rate capability and cycling stability are also achieved by enhanced surface charge storage, fast electron/ionic transportation, and improved structural stability, benifiting from the subtle structure engineering. Abstract Anodes involving conversion and alloying reaction mechanisms are attractive for potassium‐ion batteries (PIBs) due to their high theoretical capacities. However, serious volume change and metal aggregation upon potassiation/depotassiation usually cause poor electrochemical performance. Herein, few‐layered SnS2 nanosheets supported on reduced graphene oxide ([email protected]) are fabricated and investigated as anode material for PIBs, showing high specific capacity (448 mAh g−1 at 0.05 A g−1), high rate capability (247 mAh g−1 at 1 A g−1), and improved cycle performance (73% capacity retention after 300 cycles). In this composite electrode, SnS2 nanosheets undergo sequential conversion (SnS2 to Sn) and alloying (Sn to K4Sn23, KSn) reactions during potassiation/depotassiation, giving rise to a high specific capacity. Meanwhile, the hybrid ultrathin nanosheets enable fast K storage kinetics and excellent structure integrity because of fast electron/ionic transportation, surface capacitive‐dominated charge storage mechanism, and effective accommodation for volume variation. This work demonstrates that K storage performance of alloy and conversion‐based anodes can be remarkably promoted by subtle structure engineering.

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Graphene‐Encapsulated FeS2 in Carbon Fibers as High Reversible Anodes for Na+/K+ Batteries in a Wide Temperature Range

2019-03-12T10:34:26+00:00March 12th, 2019|Categories: Publications|Tags: , |

[email protected]@carbon nanofiber is synthesized, showing high rate capability in Na‐ion (305.5 mAh g−1 at 3 A g−1) and K‐ion (120 mAh g−1 at 1 A g−1) half‐cells. In particular, they deliver stable Na+ storage behavior at low temperatures (0 and −20 °C), and the [email protected]@carbon nanofiber//Na3V2(PO4)3 Na‐ion full‐cells exhibit remarkable capacity and energy density under room/low temperature. Abstract Developing low cost, long life, and high capacity rechargeable batteries is a critical factor towards developing next‐generation energy storage devices for practical applications. Therefore, a simple method to prepare graphene‐coated FeS2 embedded in carbon nanofibers is employed; the double protection from graphene coating and carbon fibers ensures high reversibility of FeS2 during sodiation/desodiation and improved conductivity, resulting in high rate capacity and long‐term life for Na+ (305.5 mAh g−1 at 3 A g−1 after 2450 cycles) and K+ (120 mAh g−1 at 1 A g−1 after 680 cycles) storage at room temperature. Benefitting from the enhanced conductivity and protection on graphene‐encapsulated FeS2 nanoparticles, the composites exhibit excellent electrochemical performance under low temperature (0 and −20 °C), and temperature tolerance with stable capacity as sodium‐ion half‐cells. The Na‐ion full‐cells based on the above composites and Na3V2(PO4)3 can afford reversible capacity of 95 mAh g−1 at room temperature. Furthermore, the full‐cells deliver promising discharge capacity (50 mAh g−1 at 0 °C, 43 mAh g−1 at −20 °C) and high energy density at low temperatures. Density functional theory calculations imply that graphene coating can effectively decrease the Na+ diffusion barrier between FeS2 and graphene heterointerface

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Multilevel Microstructured Flexible Pressure Sensors with Ultrahigh Sensitivity and Ultrawide Pressure Range for Versatile Electronic Skins

2019-03-12T10:34:24+00:00March 12th, 2019|Categories: Publications|Tags: |

Compared with other microstructured flexible pressure sensors, this unique multilevel microstructure fabricated via a two‐step sandpaper‐molding method exhibits ultrahigh sensitivity and can detect subtle and large pressure over an ultrawide testing range, which can cover the entire expected pressure regime for practical applications. This sensor is promising for applications in wearable electronics and human health monitoring. Abstract Flexible pressure sensors as electronic skins have attracted wide attention to their potential applications for healthcare and intelligent robotics. However, the tradeoff between their sensitivity and pressure range restricts their practical applications in various healthcare fields. Herein, a cost‐effective flexible pressure sensor with an ultrahigh sensitivity over an ultrawide pressure‐range is developed by combining a sandpaper‐molded multilevel microstructured polydimethylsiloxane and a reduced oxide graphene film. The unique multilevel microstructure via a two‐step sandpaper‐molding method leads to an ultrahigh sensitivity (2.5–1051 kPa−1) and can detect subtle and large pressure over an ultrawide range (0.01–400 kPa), which covers the overall pressure regime in daily life. Sharp increases in the contact area and additional contact sites caused by the multilevel microstructures jointly contribute to such unprecedented performance, which is confirmed by in situ observation of the gap variations and the contact states of the sensor under different pressures. Examples of the flexible pressure sensors are shown in potential applications involving the detection of various human physiological signals, such as breathing rate, vocal‐cord vibration, heart rate, wrist pulse, and foot plantar pressure. Another object manipulation application is also demonstrated, where the material shows its great potential as

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Overall Water Splitting: Cobalt Phosphides Nanocrystals Encapsulated by P‐Doped Carbon and Married with P‐Doped Graphene for Overall Water Splitting (Small 10/2019)

2019-03-12T10:34:22+00:00March 12th, 2019|Categories: Publications|Tags: , |

Utilizing pre‐synthesized supramolecular gels and a controllable thermal conversion technique, Yue Lin, Min Han, and co‐workers prepare three kinds of cobalt phosphides nanocrystals encapsulated by P‐doped carbon (PC) and “married” with P‐doped graphene (PG) nanohybrids. Compared with their pure phase counterparts, the mixed‐phase nanohybrids manifest better electrocatalytic performance toward overall water splitting (OWS). This work sheds light on the optimization of transition metal phosphides nanostructures based on phase engineering, and promotes their applications in OWS or other renewable energy options.

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Toward High Power‐High Energy Sodium Cathodes: A Case Study of Bicontinuous Ordered Network of 3D Porous Na3(VO)2(PO4)2F/rGO with Pseudocapacitance Effect

2019-03-12T10:34:19+00:00March 12th, 2019|Categories: Publications|Tags: , , |

A bicontinuous ordered network of 3D porous Na3(VO)2(PO4)2F/reduced graphene oxide (NVOPF/rGO) is prepared by a two‐step strategy (solvothermal plus electrostatic spray deposition method). Such electrodes exhibit excellent rate capability and cycling stability for both half cell and full cell, as well as a significant contribution of pseudocapacitance, resulting in real high power‐high energy sodium batteries. Abstract Developing high power‐high energy electrochemical energy storage systems is an ultimate goal in the energy storage field, which is even more difficult but significant for low‐cost sodium ion batteries. Here, fluoride is successfully prepared by the electrostatic spray deposition (ESD) technique, which greatly expands the application scope of ESD. A two‐step strategy (solvothermal plus ESD method) is proposed to construct a bicontinuous ordered network of 3D porous Na3(VO)2(PO4)2F/reduced graphene oxide (NVOPF/rGO). This two‐step strategy makes sure that NVOPF can be prepared by ESD, since it avoids the loss of F element during synthesis. The obtained NVOPF particles are as small as 15 nm, and the carbon content is only 3.5% in the final nanocomposite. Such a bicontinuous ordered network and small size of electroactive particles lead to the significant contribution of the pseudocapacitance effect to sodium storage, resulting in real high power‐high energy sodium cathodes. The cathode exhibits excellent rate capability and cycling stability, whose rate performance is one of the best ever reported in both half cells and full cells. Moreover, this work provides a general and promising strategy for developing high power‐high energy electrode materials for various electrochemical energy storage systems.

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Engineering Valley Polarization of Monolayer WS2: A Physical Doping Approach

2019-03-12T10:34:18+00:00March 12th, 2019|Categories: Publications|Tags: |

Here, a sizable valley polarization (P c) is obtained by in‐situ electrostatic and optical doping approaches. More than threefold enhancement of P c in monolayer WS2 at 80 K and off‐resonance excitation is obtained, which is competitive with previously reported values at cryogenic temperature and high magnetic field. The enhancement is attributed to the carrier screening effect which suppresses intervalley scattering process. Abstract The emerging field of valleytronics has boosted intensive interests in investigating and controlling valley polarized light emission of monolayer transition metal dichalcogenides (1L TMDs). However, so far, the effective control of valley polarization degree in monolayer TMDs semiconductors is mostly achieved at liquid helium cryogenic temperature (4.2 K), with the requirements of high magnetic field and on‐resonance laser, which are of high cost and unwelcome for applications. To overcome this obstacle, it is depicted that by electrostatic and optical doping, even at temperatures far above liquid helium cryogenic temperature (80 K) and under off‐resonance laser excitation, a competitive valley polarization degree of monolayer WS2 can be achieved (more than threefold enhancement). The enhanced polarization is understood by a general doping dependent valley relaxation mechanism, which agrees well with the unified theory of carrier screening effects on intervalley scattering process. These results demonstrate that the tunability corresponds to an effective magnet field of ≈10 T at 4.2 K. This work not only serves as a reference to future valleytronic studies based on monolayer TMDs with various external or native carrier densities, but also provides an alternative approach toward

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Bundled Defect‐Rich MoS2 for a High‐Rate and Long‐Life Sodium‐Ion Battery: Achieving 3D Diffusion of Sodium Ion by Vacancies to Improve Kinetics

2019-03-12T10:34:16+00:00March 12th, 2019|Categories: Publications|Tags: , |

Bundled defect‐rich MoS2 is achieved by quenching MoS2 sheet. Na+ can cross MoS2 layers by vacancies and is not limited to diffusion along the layer, realizing 3D diffusion for high rate capability. The bundled architecture reduces the stack of sheets with a superior cycle life, illustrating the capacities of 350 and 272 mAh g−1 at 2 and 5 A g−1 after 1000 cycles. Abstract Molybdenum disulfide (MoS2), a 2D‐layered compound, is regarded as a promising anode for sodium‐ion batteries (SIBs) due to its attractive theoretical capacity and low cost. The main challenges associated with MoS2 are the low rate capability suffering from the sluggish kinetics of Na+ intercalation and the poor cycling stability owning to the stack of MoS2 sheets. In this work, a unique architecture of bundled defect‐rich MoS2 (BD‐MoS2) that consists of MoS2 with large vacancies bundled by ultrathin MoO3 is achieved via a facile quenching process. When employed as anode for a SIB, the BD‐MoS2 electrode exhibits an ultrafast charge/discharge due to the pseudocapacitive‐controlled Na+ storage mechanism in it. Further experimental and theoretical calculations show that Na+ is able to cross the MoS2 layer by vacancies, not only limited to diffusion along the layer, thus realizing a 3D Na+ diffusion with faster kinetics. Meanwhile, the bundling architecture reduces the stack of sheets with a superior cycle life illustrating the highly reversible capacities of 350 and 272 mAh g−1 at 2 and 5 A g−1 after 1000 cycles.

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Adhesive Hemostatic Conducting Injectable Composite Hydrogels with Sustained Drug Release and Photothermal Antibacterial Activity to Promote Full‐Thickness Skin Regeneration During Wound Healing

2019-03-12T10:34:14+00:00March 12th, 2019|Categories: Publications|Tags: , |

A series of hydrogel dressings with multifunctions including adhesive hemostatic antioxidative conductive photothermal antibacterial property based on hyaluronic acid‐graft‐dopamine and reduced graphene oxide (rGO) with a H2O2/HPR (horseradish peroxidase) system is prepared and the high promotion repair effect for full‐thickness skin wound regeneration confirms their great potential for clinical application. Abstract Developing injectable nanocomposite conductive hydrogel dressings with multifunctions including adhesiveness, antibacterial, and radical scavenging ability and good mechanical property to enhance full‐thickness skin wound regeneration is highly desirable in clinical application. Herein, a series of adhesive hemostatic antioxidant conductive photothermal antibacterial hydrogels based on hyaluronic acid‐graft‐dopamine and reduced graphene oxide (rGO) using a H2O2/HPR (horseradish peroxidase) system are prepared for wound dressing. These hydrogels exhibit high swelling, degradability, tunable rheological property, and similar or superior mechanical properties to human skin. The polydopamine endowed antioxidant activity, tissue adhesiveness and hemostatic ability, self‐healing ability, conductivity, and NIR irradiation enhanced in vivo antibacterial behavior of the hydrogels are investigated. Moreover, drug release and zone of inhibition tests confirm sustained drug release capacity of the hydrogels. Furthermore, the hydrogel dressings significantly enhance vascularization by upregulating growth factor expression of CD31 and improve the granulation tissue thickness and collagen deposition, all of which promote wound closure and contribute to a better therapeutic effect than the commercial Tegaderm films group in a mouse full‐thickness wounds model. In summary, these adhesive hemostatic antioxidative conductive hydrogels with sustained drug release property to promote complete skin regeneration are an excellent wound dressing for full‐thickness skin repair.

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Construction of Large‐Area Ultrathin Conductive Metal–Organic Framework Films through Vapor‐Induced Conversion

2019-03-12T10:34:09+00:00March 12th, 2019|Categories: Publications|Tags: |

A new vapor‐induced method, to construct centimeter‐sized Ni3(HITP)2 films with well‐controlled thickness is designed. The substrate is raised up from bottom of water to hold up films integrally. The stripping method greatly improves the surface roughness R q without loss of conductivity and endows the film with excellent elasticity and flexibility. Abstract On account of unique characteristics, the integration of metal–organic frameworks as active materials in electronic devices attracts more and more attention. The film thickness, uniformity, area, and roughness are all fatal factors limiting the development of electrical and optoelectronic applications. However, research focused on ultrathin free‐standing films is in its infancy. Herein, a new method, vapor‐induced method, is designed to construct centimeter‐sized Ni3(HITP)2 films with well‐controlled thickness (7, 40, and 92 nm) and conductivity (0.85, 2.23, and 22.83 S m−1). Further, traditional transfer methods are tactfully applied to metal–organic graphene analogue (MOGA) films. In order to maintain the integrity of films, substrates are raised up from bottom of water to hold up films. The stripping method greatly improves the surface roughness R q (root mean square roughness) without loss of conductivity and endows the film with excellent elasticity and flexibility. After 1000 buckling cycles, the conductance shows no obvious decrease. Therefore, the work may open up a new avenue for flexible electronic and magnetic devices based on MOGA.

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Scalable Production of Nanographene and Doping via Nondestructive Covalent Functionalization

2019-03-12T10:34:07+00:00March 12th, 2019|Categories: Publications|

Scalable and efficient production of high‐quality nanographene is achieved using liquid phase exfoliation with sodium hypochlorite. Subsequent functionalization of the nanographene with a triazine derivative leads to n‐type doping while maintaining the sp2 conjugation of the nanographene, leading to enhanced conductivity. The triazine groups simultaneously offer sites for chemical postmodification for a wide range of applications. Abstract A new method for top‐down, one‐pot, gram‐scale production of high quality nanographene by incubating graphite in a dilute sodium hypochlorite solution at only 40 °C is reported here. The produced sheets have only 4 at% oxygen content, comparable with nanographene grown by chemical vapor deposition. The nanographene sheets are covalently functionalized using a nondestructive nitrene [2+1] cycloaddition reaction that preserves their π‐conjugated system. Statistical analyses of Raman spectroscopy and X‐ray photoelectron spectroscopy indicate a low number of sp3 carbon atoms on the order of 2% before and 4% after covalent functionalization. The nanographene sheets are significantly more conductive than conventionally prepared nanographene oxide, and conductivity further increases after covalent functionalization. The observed doping effects and theoretical studies suggest sp2 hybridization for the carbon atoms involved in the [2+1] cycloaddition reaction leading to preservation of the π‐conjugated system and enhancing conductivity via n‐type doping through the bridging N‐atom. These methods are easily scalable, which opens the door to a mild and efficient process to produce high quality nanographenes and covalently functionalize them while retaining or improving their physicochemical properties.

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