Showing papers by "Mingwei Chen published in 2015"
TL;DR: It is reported that nitrogen and sulfur co-doping leads to high catalytic activity of nanoporous graphene in HER at low operating potential, comparable to the best Pt-free HER catalyst, 2D MoS2 .
Abstract: Chemical doping has been demonstrated to be an effective way to realize new functions of graphene as metal-free catalyst in energy-related electrochemical reactions. Although efficient catalysis for the oxygen reduction reaction (ORR) has been achieved with doped graphene, its performance in the hydrogen evolution reaction (HER) is rather poor. In this study we report that nitrogen and sulfur co-doping leads to high catalytic activity of nanoporous graphene in HER at low operating potential, comparable to the best Pt-free HER catalyst, 2D MoS2 . The interplay between the chemical dopants and geometric lattice defects of the nanoporous graphene plays the fundamental role in the superior HER catalysis.
795 citations
TL;DR: The novel 3D nanoporous graphene demonstrates a highly energy-effective steam generation with an energy conversation of 80% in a heat generator to convert solar illumination into high-energy steam.
Abstract: Multifunctional nanoporous graphene is realized as a heat generator to convert solar illumination into high-energy steam. The novel 3D nanoporous graphene demonstrates a highly energy-effective steam generation with an energy conversation of 80%.
722 citations
TL;DR: In this article, the growth of high-quality monolayer MoS2 with control over lattice orientation has been studied and shown to be composed of coalescing single islands with limited numbers of lattice orientations due to an epitaxial growth mechanism.
Abstract: Two-dimensional semiconductors such as MoS2 are an emerging material family with wide-ranging potential applications in electronics, optoelectronics, and energy harvesting. Large-area growth methods are needed to open the way to applications. Control over lattice orientation during growth remains a challenge. This is needed to minimize or even avoid the formation of grain boundaries, detrimental to electrical, optical, and mechanical properties of MoS2 and other 2D semiconductors. Here, we report on the growth of high-quality monolayer MoS2 with control over lattice orientation. We show that the monolayer film is composed of coalescing single islands with limited numbers of lattice orientation due to an epitaxial growth mechanism. Optical absorbance spectra acquired over large areas show significant absorbance in the high-energy part of the spectrum, indicating that MoS2 could also be interesting for harvesting this region of the solar spectrum and fabrication of UV-sensitive photodetectors. Even though t...
656 citations
TL;DR: A simple and general method for covalent functionalization of two-dimensional transition metal dichalcogenide nanosheets (MoS, WS and MoSe) is described, which shows that it renders the metallic 1T phase semiconducting, and gives it strong and tunable photoluminescence and gate modulation in field-effect transistors.
Abstract: Chemical functionalization of low-dimensional materials such as nanotubes, nanowires and graphene leads to profound changes in their properties and is essential for solubilizing them in common solvents. Covalent attachment of functional groups is generally achieved at defect sites, which facilitate electron transfer. Here, we describe a simple and general method for covalent functionalization of two-dimensional transition metal dichalcogenide nanosheets (MoS₂, WS₂ and MoSe₂), which does not rely on defect engineering. The functionalization reaction is instead facilitated by electron transfer between the electron-rich metallic 1T phase and an organohalide reactant, resulting in functional groups that are covalently attached to the chalcogen atoms of the transition metal dichalcogenide. The attachment of functional groups leads to dramatic changes in the optoelectronic properties of the material. For example, we show that it renders the metallic 1T phase semiconducting, and gives it strong and tunable photoluminescence and gate modulation in field-effect transistors.
619 citations
TL;DR: Experimental and theoretical investigations suggest that the unusual catalytic performance of this catalyst is due to sp-d orbital charge transfer between the Ni dopants and the surrounding carbon atoms.
Abstract: Single-atom nickel dopants anchored to three-dimensional nanoporous graphene can be used as catalysts of the hydrogen evolution reaction (HER) in acidic solutions. In contrast to conventional nickel-based catalysts and graphene, this material shows superior HER catalysis with a low overpotential of approximately 50 mV and a Tafel slope of 45 mV dec(-1) in 0.5 M H2SO4 solution, together with excellent cycling stability. Experimental and theoretical investigations suggest that the unusual catalytic performance of this catalyst is due to sp-d orbital charge transfer between the Ni dopants and the surrounding carbon atoms. The resultant local structure with empty C-Ni hybrid orbitals is catalytically active and electrochemically stable.
599 citations
TL;DR: A special two-day international workshop on high-entropy alloys was held in Guiyang, China, in December 2014 as mentioned in this paper to discuss the scientific issues and challenges to foster international collaborations, and to identify future directions.
335 citations
TL;DR: A layered composite with P2 and O3 integration is proposed toward a sodium-ion battery with high energy density and long cycle life, which can deliver a high reversible capacity and good capacity retention over 150 times of sodium extraction and insertion.
Abstract: A layered composite with P2 and O3 integration is proposed toward a sodium-ion battery with high energy density and long cycle life. The integration of P2 and O3 structures in this layered oxide is clearly characterized by XRD refinement, SAED and HAADF and ABF-STEM at atomic resolution. The biphase synergy in this layered P2+O3 composite is well established during the electrochemical reaction. This layered composite can deliver a high reversible capacity with the largest energy density of 640 mAh g−1, and it also presents good capacity retention over 150 times of sodium extraction and insertion.
305 citations
TL;DR: It is shown that a Se-deficit in single layers of MoSe2 grown by molecular beam epitaxy gives rise to a dense network of mirror-twin-boundaries (MTBs) decorating the 2D-grains, and that MTBs are thermodynamically stable structures in Se- deficient sheets.
Abstract: We study the atomic scale microstructure of nonstoichiometric two-dimensional (2D) transition metal dichalcogenide MoSe2–x by employing aberration-corrected high-resolution transmission electron microscopy. We show that a Se-deficit in single layers of MoSe2 grown by molecular beam epitaxy gives rise to a dense network of mirror-twin-boundaries (MTBs) decorating the 2D-grains. With the use of density functional theory calculations, we further demonstrate that MTBs are thermodynamically stable structures in Se-deficient sheets. These line defects host spatially localized states with energies close to the valence band minimum, thus giving rise to enhanced conductance along straight MTBs. However, electronic transport calculations show that the transmission of hole charge carriers across MTBs is strongly suppressed due to band bending effects. We further observe formation of MTBs during in situ removal of Se atoms by the electron beam of the microscope, thus confirming that MTBs appear due to Se-deficit, and...
206 citations
TL;DR: In this article, a stable symmetric sodium-ion battery based on the bipolar active O3-type material, Na0.8Ni0.4Ti0.6O2, is developed.
Abstract: Based on low-cost and rich resources, sodium-ion batteries have been regarded as a promising candidate for next-generation energy storage batteries in the large-scale energy applications of renewable energy and smart grids. However, there are some critical drawbacks limiting its application, such as safety and stability problems. In this work, a stable symmetric sodium-ion battery based on the bipolar, active O3-type material, Na0.8Ni0.4Ti0.6O2, is developed. This bipolar material shows a typical O3-type layered structure, containing two electrochemically active transition metals with redox couples of Ni4+/Ni2+ and Ti4+/Ti3+, respectively. This Na0.8Ni0.4Ti0.6O2-based symmetric cell exhibits a high average voltage of 2.8 V, a reversible discharge capacity of 85 mA h g−1, 75% capacity retention after 150 cycles and good rate capability. This full symmetric cell will greatly contribute to the development of room-temperature sodium-ion batteries with a view towards safety, low cost and long life, and it will stimulate further research on symmetric cells using the same active materials as both cathode and anode.
199 citations
TL;DR: Freestanding nanoporous N-doped graphene with encapsulated RuO2 nanoparticles is developed as a cathode for rechargeable Li-O2 batteries, and the stabilized metal oxide catalyst reduces charge overpotentials enabling high-efficiency rechargeables with a long cycling lifetime.
Abstract: Freestanding nanoporous N-doped graphene with encapsulated RuO2 nanoparticles is developed as a cathode for rechargeable Li-O2 batteries. The stabilized metal oxide catalyst reduces charge overpotentials enabling high-efficiency rechargeable Li-O2 batteries with a long cycling lifetime. This has important implications for the development of highly stable and catalytically active graphene-based cathodes for rechargeable Li-O2 batteries.
188 citations
TL;DR: In this paper, a nominal single-phase, high-entropy alloy (HEA) was characterized using scanning transmission electron microscopy (STEM) combined with atom probe tomography (APT).
TL;DR: The full cell based on this bipolar electrode exhibits well-defined voltage plateaus near 3.10 V, which is the highest average voltage in the symmetric cells.
Abstract: Recently, there has been great interest in developing advanced sodium-ion batteries for large-scale application. Most efforts have concentrated on the search for high-performance electrode materials only in sodium half-cells. Research on sodium full cells for practical application has encountered many problems, such as insufficient cycles with rapid capacity decay, low safety, and low operating voltage. Herein, we present a layered P2-Na0.66 Ni0.17 Co0.17 Ti0.66 O2 , as both an anode (ca. 0.69 V versus Na(+) /Na) and as a high-voltage cathode (ca. 3.74 V versus Na(+) /Na). The full cell based on this bipolar electrode exhibits well-defined voltage plateaus near 3.10 V, which is the highest average voltage in the symmetric cells. It also shows the longest cycle life (75.9 % capacity retention after 1000 cycles) in all sodium full cells, a usable capacity of 92 mAh g(-1) , and superior rate capability (65 mAh g(-1) at a high rate of 2C).
TL;DR: In this article, a simple approach to fabricate aligned bimetallic Pt-Cu microwires with a three-dimensional nanoporous structure, tunable composition, and high catalytic activity by dealloying a dilute Pt3Cu97 precursor was reported.
Abstract: We report a simple approach to fabricate aligned bimetallic Pt–Cu microwires with a three-dimensional nanoporous structure, tunable composition, and high catalytic activity by dealloying a dilute Pt3Cu97 precursor. Each microwire possesses inherent ultrafine nanoporous structure with uniformly distributed Pt–Cu alloy ligaments and nanopores with a dimension of ∼2 nm. Electrochemical measurements manifest that the nanoporous Pt–Cu microwires have significantly enhanced electrocatalytic activities compared with a commercial Pt/C nanoparticulate catalyst. With evident advantages of facile preparation and enhanced catalytic performance together with low material costs, the nanoporous Pt–Cu microwires hold great promise as a high-performance catalyst for electrochemical energy conversion.
TL;DR: A novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates is reported, using the integrated experimental and theoretical approaches to provide a new alloy-design strategy using the novel concept of hierarchical precipitate and the fundamental science for developing creep-resistant ferritic alloys.
Abstract: There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones. These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. The present research will broaden the applications of ferritic alloys to higher temperatures.
TL;DR: Microscale supercapapcitors based on hierarchical nanoporous hybrid electrodes consisting of 3D bicontinuous nanoporous gold and pseudocapacitive manganese oxide deliver an excellent stack capacitance and a retained high power density.
Abstract: Microscale supercapapcitors based on hierarchical nanoporous hybrid electrodes consisting of 3D bicontinuous nanoporous gold and pseudocapacitive manganese oxide deliver an excellent stack capacitance of 99.1 F cm-3 and a high energy density of 12.7 mW h cm-3 with a retained high power density of 46.6 W cm-3.
TL;DR: A novel multicomponent mixed-valence oxyhydroxide-based electrode synthesized by electrochemical polarization of a de-alloyed nanoporous NiCuMn alloy possesses an extraordinarily wide working-potential window of 1.8 V in an aqueous electrolyte, which far exceeds the theoretically stable window of water.
Abstract: We report a novel multicomponent mixed-valence oxyhydroxide-based electrode synthesized by electrochemical polarization of a de-alloyed nanoporous NiCuMn alloy. The multicomponent oxyhydroxide has a high specific capacitance larger than 627 F cm−3 (1097±95 F g−1) at a current density of 0.25 A cm−3, originating from multiple redox reactions. More importantly, the oxyhydroxide electrode possesses an extraordinarily wide working-potential window of 1.8 V in an aqueous electrolyte, which far exceeds the theoretically stable window of water. The realization of both high specific capacitance and high working-potential windows gives rise to a high energy density, 51 mWh cm−3, of the multicomponent oxyhydroxide-based supercapacitor for high-energy and high-power applications.
TL;DR: In this paper, dealloyed nanoporous metals can realize the intrinsic lithium storage performance of transition metal oxides by forming oxide/metal composites, which can be directly used as anodes and show highly reversible specific capacity with high-rate capability and long cyclic stability.
Abstract: Lithium-ion batteries (LIBs) have been intensively studied to meet the increased demands for the high energy density of portable electronics and electric vehicles. The low specific capacity of the conventional graphite based anodes is one of the key factors that limit the capacity of LIBs. Transition metal oxides, such as NiO, MnO2 and Fe3O4, are known to be promising anode materials that are expected to improve the specific capacities of LIBs for several times. However, the poor electrical conductivity of these oxides significantly restricts the lithium ion storage and charge/discharge rate. Here we report that dealloyed nanoporous metals can realize the intrinsic lithium storage performance of the oxides by forming oxide/metal composites. Without any organic binder, conductive additive and additional current collector, the hybrid electrodes can be directly used as anodes and show highly reversible specific capacity with high-rate capability and long cyclic stability.
TL;DR: Li et al. as mentioned in this paper used Suzuki segregation of alloying atoms to prevent the formation of stacking-fault ribbons in the alloy matrix, which can slow down the coarsening of the nano-sized γ′ phase at high temperatures.
Abstract: The properties of superalloys are typically deteriorated by the coarsening of the nano-sized γ′ phase, which is the primary strengthening component at high temperatures Stabilizing the γ′ phase represents one of the key challenges in developing next-generation superalloys Herein, we fabricate a cobalt-nickel-based superalloy with a nanoscale coherent γ′ phase, (Ni,Co)3(Al,Ti,Nb), which is isolated by stacking-fault ribbons in the alloy matrix as a result of the Suzuki segregation of alloying atoms Additionally, we demonstrate that this new nanostructure can slow down the coarsening of the γ′ phase at high temperatures As a result, the cobalt-nickel-based superalloy displays considerably high tensile yield points, exceeding 1650 MPa at room temperature and 1250 MPa at 973 K, which are markedly higher than those of the commonly used nickel- and cobalt-based superalloys This study thereby paves a new path for developing superalloys with exceptional mechanical performance and thermal stability By using a novel nanostructure, a team has made a cobalt-based superalloy with a high tensile yield point whose γ' phase resists coarsening Coarsening of the nanoscale γ' phase of superalloys — the process by which large particles grow at the expense of smaller ones — tends to degrade the properties of superalloys since the γ' phase is the main strengthening component at high temperatures By isolating the γ' phase through forming stacking-fault ribbons in the alloy matrix via Suzuki segregation of the alloying atoms, Yunping Li of Central South University in China and collaborators at Tohoku University in Japan realized a cobalt-nickel-based superalloy with a tensile yield point of 1,650 megapascals at room temperature (1,250 megapascals at 973 kelvin) They consider this method to be promising for realizing superalloys with superior mechanical properties and thermal stability A large number of multilayered stacking faults are detected along {111} planes during aging (arrows in a) of present superalloy Every γ′ phase particle is isolated by multilayered stacking-fault ribbons and grows slightly The coarsening rate of the γ′ phase decreases significantly after plastic deformation, implying that the formation of multilayered stacking-fault ribbons as a consequence of Suzuki segregation can obviously retard the coarsening of γ′ phase in this novel alloy
TL;DR: In this article, a free-standing nanoporous YNiCo metal/metal-oxide composite with hierarchical porosity is fabricated by chemically dealloying Al 85 Y 6 Ni 6 Co 3 metallic glass in alkaline solutions.
TL;DR: In this article, the authors exploit the high oxygen evolution reaction activities of oxides by incorporating insulator oxides into the pore channels of highly conductive nanoporous gold to form three-dimensional nanoporous core-shell composites.
Abstract: Lithium–oxygen batteries have attracted considerable attention due to their expected specific energy being far higher than that of lithium-ion batteries. The high charge overpotentials of the cathodic oxygen evolution reaction of insulator lithium peroxide is one of the critical challenges for practical implementation of lithium–oxygen batteries, which results in low energy efficiency and poor stability of cathodes and electrolytes. Transition metal oxides are known to be the most active electrocatalysts that can dramatically decrease the charging overpotentials of rechargeable lithium–air batteries. However, the poor electrical conductivity of these oxide electrocatalysts, such as RuO2, MnO2 and Co3O4, limits the charge transport of cathodic reactions and the full utilization of their catalytic activities. Herein, we exploit the high oxygen evolution reaction activities of oxides by incorporating insulator oxides into the pore channels of highly conductive nanoporous gold to form three-dimensional nanoporous core–shell composites. The hybrid catalysts as the cathodes of rechargeable lithium–oxygen batteries show highly reversible cathodic reactions at extremely lower overpotentials for high efficiency lithium–air batteries, arising from the synergistic effect of high conductive nanoporous gold (NPG) and catalytically active metal oxides.
TL;DR: In this article, the size induced brittle-to-ductile transition in single-crystal aluminum nitride (AlN) was reported, showing metal-like plastic flow under room-temperature uniaxial compression.
TL;DR: In this paper, a ternary Zr-Cu-Al alloy was observed in-situ by high energy synchrotron radiation X-ray diffraction in the temperature range from above the liquidus Tliq to well below the glass transition temperature Tg.
TL;DR: The composition mediated serration dynamics in Zr-based bulk metallic glasses (BMGs) is investigated by statistics analyses of the elastic energy density, and free volumes during shear-banding as mentioned in this paper.
Abstract: The composition mediated serration dynamics in Zr-based bulk metallic glasses (BMGs) is investigated by statistics analyses of the elastic-energy density, and free volumes during shear-banding are beneficial to understand serrated-flow behavior. The amplitude and elastic-energy density display a gradually increasing and then decreasing trend with increasing the content of Zr. It is based on the free-volume theory describing the atomic-level structure of ternary Zr-Cu-Al BMGs. The good agreement between the molecular dynamics simulation and experimental results provides evidence for the variation of free volumes as the elementary mechanism of composition mediated serration dynamics.
TL;DR: In this paper, a metallic glass (MG)-based microscanner is reported with MG as the material for the moving torsion bars, which offers, for the first time, an ultralarge rotating angle of 146° with power consumption lowered to the microwatt range.
Abstract: Microelectromechanical system (MEMS) actuators essentially have movable silicon structures where the mechanical motion can be activated electronically. The microscanner is one of the most successfully commercialized MEMS devices which are widely used for collecting optical information, manipulating light, and displaying images. While silicon is abundant, it is also brittle and stiff and when microprocessed, defects are not uncommon. These defects result in weakness under torsional stress and this has been the key factor limiting the scanning performance of the microscanner. Here a metallic glass (MG)-based microscanner is reported with MG as the material for the moving torsion bars. The low elastic modulus, high fracture toughness, and high strength of MG offers, for the first time, an ultralarge rotating angle of 146° with power consumption lowered to the microwatt range, and a smaller driving force and better actuation performance, than conventional single crystal silicon and polycrystalline silicon. The high spatial resolution and large scanning field of the MG-based microscanner are demonstrated in the tomographic imaging of a human finger. This development of an MG-based MEMS possibly opens a new field of low-powered MEMS devices with extreme actuation and enhanced sensing.
TL;DR: In this article, the authors investigated the thermal coarsening of nanoporous gold (NPG) by in situ environmental transmission electron microscopy and found that NPG has high structural stability against heat treatment in vacuum.
Abstract: In order to investigate environmental effects on the ligament/pore coarsening of nanoporous gold (NPG), we studied the thermal coarsening of NPG both in air and vacuum by ex situ observation, and found that it has high structural stability against heat treatment in vacuum. To clarify the nature of this phenomenon, we investigated the thermal coarsening of NPG by in situ environmental transmission electron microscopy. At an elevated temperature (400°C), the coarsening of ligaments/pores was triggered by introducing either pure N2 or O2 gas into the transmission electron microscopy (TEM) chamber (but not by Ar gas). We thus conclude with a discussion on the mechanism for thermal coarsening of NPG. [doi:10.2320/matertrans.MF201403]
TL;DR: Nanoporous metals similar to paper in form are developed using Japanese washi paper as a template to create hierarchical porous electrodes to create trimodal nanoporous Au electrode and hierarchical NiMn electrode that achieves high electrochemical capacitance and a rapid rate of oxygen evolution.
Abstract: Nanoporous metals similar to paper in form are developed using Japanese washi paper as a template to create hierarchical porous electrodes. This method is used to create a trimodal -nanoporous Au electrode, as a well as a hierarchical NiMn electrode that achieves high electrochemical capacitance and a rapid rate of oxygen evolution.
TL;DR: In this paper, the formation of Pd-based multicomponent nanoporous metals by electrochemically dealloying the Pd80−xNixP20 metallic glasses was reported.
TL;DR: In this paper, a numerical post-processing method for removing the effect of anti-symmetric residual aberrations in high-resolution transmission electron microscopy (HRTEM) images of weakly scattering 2D-objects is presented.
TL;DR: In this article, the authors presented a new kind of giant magnetostrictive actuator; the distribution of magnetic field density was simulated by finite element simulation software (ANSYS) by changing the excitation current.
Abstract: Based on the working characteristics of giant magnetostrictive materials, this paper presents a new kind of giant magnetostrictive actuator; the distribution of magnetic field density of the giant magnetostrictive actuator is simulated by finite element simulation software (ANSYS). By changing the excitation current, the relationship between the internal magnetic field strength of giant magnetostrictive actuator and the excitation current is obtained; the research results show, with the current increasing gradually, the magnetic flux density in the giant magnetostrictive materials also increases, and then, the magnetic flux density will trend to be saturated. In addition, the effect of the additional magnetic field on magnetic flux density of giant magnetostrictive materials is also validated.
01 Aug 2015
TL;DR: In this article, the authors report fabrication and characterization of a cytochrome-c functionalized SOA biosensor built on commercially available miniaturized screen-printed electrodes made of gold microspheres.
Abstract: Superoxide anion (SOA) as a member of reactive oxygen species (ROS) group is involved in various physiological and pathological states. For instance, generation of SOA is known to increase with skeletal muscle contractile activity and fatigue. It is therefore important to selectively detect and accurately quantify the release of SOA within both physiological and pathological levels. We report fabrication and characterization of a cytochrome-c functionalized SOA biosensor built on commercially available miniaturized screen-printed electrodes made of gold microspheres. The device was first tested and calibrated in a xanthine/xanthine oxidase (XOD) system and then employed to detect SOA release from C2C12 myoblasts and myotubes upon stimulation with PMA.