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1.
Nanotechnology ; 31(27): 275404, 2020 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-32224518

RESUMO

Although there are numerous virtues for lithium sulfur batteries, the notorious shuttle effect and insulated nature are impeding their practical application. To address these issues, here we report the design and synthesis of polypyrrole coated sulfur and cobalt co-doped carbon nanocages (PSCC). It demonstrates that both the performance and stability of the PSCC assisted Li-S batteries are improved. The hollow structure of PSCC bypassed the structural collapse effectively caused by volume expansion of sulfur during the reaction and physically suppressed shuttle effect of the intermediate product polysulfide lithium (LiPSs). Also, LiPSs was also trapped to inhibit the shuttle effect due to the strong adsorption of LiPSs via PSCC. In addition, PSCC can also provide an outstanding electronic conductivity, which will facilitate the next-step reaction of the absorbed LiPSs and enhance electrochemical reaction kinetics. Thus, the excellent rate performance was obtained with high specific discharge capacities of 1300 mAh g-1 at 0.1 C and 1000 mAh g-1 at 0.5 C. Such packaged high-performance positions our design for the ideal electrochemical energy storage devices.

2.
J Phys Chem Lett ; : 1614-1621, 2020 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-32048850

RESUMO

Lubrication plays a pivotal role in reducing energy consumption and machinery wear, profoundly impacting technological and economic development and the environment. A recent study ( Erdemir , A. , et al. Nature 2016 , 536 , 67 ) reported the effective extraction of carbon-based tribofilms from lubricating oil by catalytic activation of the coating material, opening new possibilities for innovative lubrication material research and development. Here, we showcase a solute-atom-strengthened and catalytically functionalized coating design and demonstrate its implementation in a TiN-Ag solid solution film that exhibits concurrent ultralow friction and ultralow wear. Indentation tests and Raman and X-ray photoelectron spectroscopy combined with quantum mechanical simulations uncover the rare superhard nature of the TiN-Ag film along with a solute-Ag-atom-induced self-oxidation mechanism for its outstanding catalytic capacity. These findings identify an outstanding type of mechanically strong and catalytically active coating material with simultaneous superior protective and lubricating functionality, holding great promise for applications ranging from microdevices to large-scale industrial equipment.

3.
J Am Chem Soc ; 2020 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-32023049

RESUMO

The design of catalysts with high activity and robust stability for alkaline hydrogen evolution reaction (HER) remains a great challenge. Here, we report an efficient catalyst of two-dimensional bimetallene hydrides, in which H atoms stabilize the rhodium palladium bimetallene. The system exists because of the introduction of H that is in situ chemically released from the formaldehyde solution during the synthesis. This provides a highly stable catalyst based on an unstable combination of metal elements. Density functional theory calculations show the H is confined by electronic interactions and the Miedema rule of reverse stability of the RhPd alloy. The obtained catalyst exhibits outstanding alkaline HER catalytic performance with a low overpotential of 40 mV at 10 mA cm-2 and remarkable stability for over 10 h at 100 mA cm-2. The experimental results show that the confined H improve the activity, while the ultrathin sheet-like morphology yields stability. Our work provides guidance for synthesizing high-activity catalysts by confining heteroatoms into the crystal lattice of bimetallene and also a very novel mechanism for the growth of bimetallene made of highly immiscible components.

4.
Nanoscale ; 12(3): 2011-2021, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31912850

RESUMO

Unique SnO2 triple-shelled hollow cages with a well-defined cubic shape have been successfully prepared via additional deposition of polycrystalline SnO2 on hybrid Zn2SnO4/SnO2 double-shelled nanotemplates followed by removal of Zn2SnO4. Structural characterization demonstrates that SnO2 triple-shelled hollow cubes (THCs) are hierarchically composed of numerous primary nanoparticles with a size of about several nanometers. The synthetic step-dependent multilayered evolution mechanism can be addressed in terms of different hollowing strategies. Based on the unique less-agglomerated multilayered and porous configuration, the gas sensing performances of SnO2 THCs exhibit an obvious improvement of response and shortened response-recovery characteristics at their optimal working temperature, compared with those of referenced single- and double-shelled SnO2 nanostructures.

5.
Nanotechnology ; 31(13): 135403, 2020 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-31770727

RESUMO

Earth-abundant Fe2O3 is a promising material for the negative electrode of supercapacitors by virtue of its wide potential windows. However, the unsatisfactory electrical conductivity and poor ionic diffusion rate within Fe2O3 results in degraded electrochemical performance. In this work, to address these issues, we demonstrate an easy method to synthesize Fe-based zeolitic imidazolate framework (Fe-ZIF) derived α-Fe2O3@C with remarkable supercapacitive properties. The as-obtained α-Fe2O3@C electrode, with the particular benefit of dispersed distribution of carbon, enabling fast electrochemical response, presents a prospective specific capacitance of 161 Fg-1 at a current density of 1 Ag-1. Furthermore, by using the α-Fe2O3@C architecture as the negative electrode, we fabricated a supercapacitor with Na0.5MnO2 as the positive electrode. Our supercapacitor shows a high energy density of 25 Whkg-1, while the corresponding power density is 2400 Wkg-1 at a current density of 2 Ag-1.

6.
Nanotechnology ; 31(10): 105402, 2019 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-31751956

RESUMO

Clarifying the interaction between active materials and current collectors of the same electrode is crucial for understanding the electrochemical energy storage mechanism and designing high-performance supercapacitors. The interaction mechanism is mainly due to the evolution of chemical bonding. Here, we explore the chemical bonding evolution between cobalt-nickel layered double hydroxide and carbon fiber paper by using ex situ x-ray photoelectron spectroscopy during redox reaction. The results reveal that chemical bonding corresponds to more ionic states at the lowest potential and more covalent states at the highest potential. Attributed to the formation of C-O-Metal (Co, Ni) chemical bonds, high capacitance with enhanced stability and rate capability is obtained. The Co-Ni layered double hydroxide electrode exhibits a high areal and mass specific capacitance of 0.55 and 952 F g-1 at a low mass loading of 0.58 mg cm-2. At a high mass loading of 3.59 mg cm-2, high areal and mass specific capacitance of 3.24 F cm-2 and 811 F g-1 are obtained. Based on this, a hybrid supercapacitor is fabricated with high-mass-loading Co-Ni layered double hydroxide and active carbon as positive and negative electrodes, respectively. As a result, this device delivers a prominent energy density of 20.9 Wh cm-3 at a power density of 0.12 W cm-3.

7.
Nat Commun ; 10(1): 5231, 2019 11 19.
Artigo em Inglês | MEDLINE | ID: mdl-31745074

RESUMO

The grand challenge in the development of atomically dispersed metallic catalysts is their low metal-atom loading density, uncontrollable localization and ambiguous interactions with supports, posing difficulty in maximizing their catalytic performance. Here, we achieve an interface catalyst consisting of atomic cobalt array covalently bound to distorted 1T MoS2 nanosheets (SA Co-D 1T MoS2). The phase of MoS2 transforming from 2H to D-1T, induced by strain from lattice mismatch and formation of Co-S covalent bond between Co and MoS2 during the assembly, is found to be essential to form the highly active single-atom array catalyst. SA Co-D 1T MoS2 achieves Pt-like activity toward HER and high long-term stability. Active-site blocking experiment together with density functional theory (DFT) calculations reveal that the superior catalytic behaviour is associated with an ensemble effect via the synergy of Co adatom and S of the D-1T MoS2 support by tuning hydrogen binding mode at the interface.

8.
Small ; 15(50): e1905050, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31721434

RESUMO

Upconversion near-infrared (NIR) fluorescent carbon dots (CDs) are important for imaging applications. Herein, thermally activated upconversion photoluminescence (UCPL) in the NIR region, with an emission peak at 784 nm, which appears under 808 nm continuous-wave laser excitation, are realized in the NIR absorbing/emissive CDs (NIR-CDs). The NIR-CDs are synthesized by microwave-assisted exfoliation of red emissive CDs in dimethylformamide, and feature single or few-layered graphene-like cores. This structure provides an enhanced contact area of the graphene-like plates in the core with the electron-acceptor carbonyl groups in dimethylformamide, which contributes to the main NIR absorption band peaked at 724 nm and a tail band in 800-850 nm. Temperature-dependent photoluminescence spectra and transient absorption spectra confirm that the UCPL of NIR-CDs is due to the thermally activated electron transitions in the excited state, rather than the multiphoton absorption process. Temperature dependent upconversion NIR luminescence imaging is demonstrated for NIR-CDs embedded in a polyvinyl pyrrolidone film, and the NIR upconversion luminescence imaging in vivo using NIR-CDs in a mouse model is accomplished.

9.
Nat Commun ; 10(1): 4472, 2019 10 02.
Artigo em Inglês | MEDLINE | ID: mdl-31578330

RESUMO

Moiré superlattices (MSLs) are modulated structures produced from homogeneous or heterogeneous 2D layers stacked with a twist angle and/or lattice mismatch. Expanding the range of available materials, methods for fabricating MSL, and realization of unique emergent properties are key challenges. Here we report a facile bottom-up synthesis of homogeneous MSL based on a wide-gap 2D semiconductor, BiOCl, using a one-pot solvothermal approach with robust reproducibility. Unlike previous MSLs usually prepared by directly stacking two monolayers, our BiOCl MSLs are realized in a scalable, direct way through chemical growth of spiral-type nanosheets driven by screw-dislocations. We find emergent properties including large band gap reduction (∼0.6 eV), two-fold increase in carrier lifetime, and strongly enhanced photocatalytic activity. First-principles calculations reveal that such unusual properties can be ascribed to the locally enhanced inter-layer coupling associated with the Moiré potential modulation. Our results demonstrate the promise of MSL materials for chemical and physical functions.

10.
ACS Nano ; 13(10): 12024-12031, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31589022

RESUMO

We realized the synthesis of carbon nanorods-monodisperse colloidal particles with a length of 50 nm and a width of 20 nm-which can be considered an addition to the family of light-emitting carbon-based nanostructures. Their anisotropic shape is determined by the use of the surfactant aminopropylisobutyl polyhedral oligomeric silsesquioxane, and their optical properties originate from domains of polycyclic aromatic hydrocarbons incorporated within an inorganic framework. The nanorods show dual polarized emission with a quantum yield of 15-20% and emission anisotropy of ∼0.3, which changes from blue (460 nm) to yellow (565 nm) depending on the excitation wavelength. These carbon nanorods expand the range of light-emitting carbon nanomaterials available for optoelectronic and biolabeling applications.

11.
ACS Nano ; 13(11): 12987-12995, 2019 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-31618006

RESUMO

Rational control of the components of noble metal alloys is paramount for achieving satisfactory electrocatalytic performances. Though transition metals are commonly used to modify noble metals, many potential elements remain to be explored. Here, we interstitially modulate hydrogen atoms into RhPd nanoparticles to boost the alkaline hydrogen evolution reaction (HER). The obtained stable RhPd-H nanoparticles exhibit pronounced alkaline HER activity with a small overpotential of 36.6 mV at 10 mA cm-2 and a low Tafel slope of 35.3 mV dec-1. The surface electronic state, bond distance, and coordination number of the Rh and Pd atoms are significantly influenced by the presence of interstitial hydrogen atoms. These modifications give RhPd-H nanoparticles a desirable hydrogen adsorption free energy, thus accelerating the hydrogen gas production. We further demonstrate that the interstitial hydrogen atom modulation strategy to improve the HER activity is universal for other Pd-based alloy nanostructures. This work presents a powerful strategy for designing efficient electrocatalysts for the HER and beyond.

12.
ACS Omega ; 4(8): 13209-13217, 2019 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-31460448

RESUMO

We explore the stability, electronic properties, and quantum capacitance of doped/co-doped graphene with B, N, P, and S atoms based on first-principles methods. B, N, P, and S atoms are strongly bonded with graphene, and all of the relaxed systems exhibit metallic behavior. While graphene with high surface area can enhance the double-layer capacitance, its low quantum capacitance limits its application in supercapacitors. This is a direct result of the limited density of states near the Dirac point in pristine graphene. We find that the triple N and S doping with single vacancy exhibits a relatively stable structure and high quantum capacitance. It is proposed that they could be used as ideal electrode materials for symmetry supercapacitors. The advantages of some co-doped graphene systems have been demonstrated by calculating quantum capacitance. We find that the N/S and N/P co-doped graphene with single vacancy is suitable for asymmetric supercapacitors. The enhanced quantum capacitance contributes to the formation of localized states near the Dirac point and/or Fermi-level shifts by introducing the dopant and vacancy complex.

13.
Nanoscale ; 11(32): 15037-15042, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-31206116

RESUMO

Interfacial contacts within electrodes largely affect electronic transport and ion migration. Nanoscale electrode materials can achieve high reactivity, but their large interfacial contact areas lead to unavoidable impedance. Herein, a Ti3C2Tx MXene was used to construct a hybrid three-dimensional electrode material with a bilayer feature via a two-step vacuum filtration process. The introduced MXene flakes contributed to the electrode capacity, increased the electronic/ionic conductivity as a conductor and current collector, and enhanced the mechanical behaviour of the electrode by acting as a substrate. Such bilayer hybrid electrode design achieved promising cycling stability, and unlock an electrode architecture that can be applied to a wide range of two-dimensional materials.

14.
Nano Lett ; 19(5): 2758-2764, 2019 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-30958673

RESUMO

Metallic 1T-phase transition metal dichalcogenides (TMDs) are of considerable interest in enhancing catalytic applications due to their abundant active sites and good conductivity. However, the unstable nature of 1T-phase TMDs greatly impedes their practical applications. Herein, we developed a new approach for the synthesis of highly stable 1T-phase Au/Pd-MoS2 nanosheets (NSs) through a metal assembly induced ultrastable phase transition for achieving a very high electrocatalytic activity in the hydrogen evolution reaction. The phase transition was evoked by a novel mechanism of lattice-mismatch-induced strain based on density functional theory (DFT) calculations. Raman spectroscopy and transmission electron microscopy (TEM) were used to confirm the phase transition on experimental grounds. A novel heterostructured 1T MoS2-Au/Pd catalyst was designed and synthesized using this mechanism, and the catalyst exhibited a 0 mV onset potential in the hydrogen evolution reaction under light illumination. Therefore, this method can potentially be used to fabricate 1T-phase TMDs with remarkably enhanced activities for different applications.

15.
Nanoscale ; 11(16): 7554-7559, 2019 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-30946418

RESUMO

Fabricating heterostructures enhances the photocatalytic performance of metal-organic frameworks (MOFs) due to their excellent light absorption and high efficient charge transfer capacity. In this study, we designed and implemented three-dimensional dendritic UiO-66-NH2@MIL-101(Fe) (UOML) heterostructures as catalysts for photocatalytic styrene oxidation. The UOML catalysts exhibited a well-matched band gap structure and efficient catalytic interface, leading to a remarkable photoexcited carrier separation and catalytic activity. Our results present a promising insight for synthesizing novel MOFs-based catalysts and their applications.

16.
Materials (Basel) ; 12(4)2019 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-30823530

RESUMO

The structure, valence state, and dielectric properties of (Ba1-xSmx)(Ti0.99Mn0.01)O3 (BSTM) (x = 0.02‒0.07) ceramics prepared via a high temperature (1400 °C/12 h) solid state reaction were investigated. A homogeneous and dense microstructure was observed in all samples. With increasing Sm content, the crystal structure changed from tetragonal (x ≤ 0.06) to cubic (x = 0.07) and unit cell volume (V0) decreased continuously, which was mainly due to the substitution of Ba2+ ions by smaller Sm3+ ions in the perovskite lattice. Electron paramagnetic resonance investigation revealed that Mn ions were reduced from high valence to low valence under the role of Sm3+ donor, and only Mn2+ ions were observed at x = 0.07. The Curie temperature (Tc) moved to lower values, from 105.5 down to 20.4 °C, and the x = 0.07 sample satisfied Y5V specification with high permittivity (ε'RT > 13,000) and low loss (tan δ < 0.03).

17.
Nat Commun ; 10(1): 665, 2019 02 08.
Artigo em Inglês | MEDLINE | ID: mdl-30737389

RESUMO

Quantum efficiencies of organic-inorganic hybrid lead halide perovskite light-emitting devices (LEDs) have increased significantly, but poor device operational stability still impedes their further development and application. All-inorganic perovskites show better stability than the hybrid counterparts, but the performance of their respective films used in LEDs is limited by the large perovskite grain sizes, which lowers the radiative recombination probability and results in grain boundary related trap states. We realize smooth and pinhole-free, small-grained inorganic perovskite films with improved photoluminescence quantum yield by introducing trifluoroacetate anions to effectively passivate surface defects and control the crystal growth. As a result, efficient green LEDs based on inorganic perovskite films achieve a high current efficiency of 32.0 cd A-1 corresponding to an external quantum efficiency of 10.5%. More importantly, our all-inorganic perovskite LEDs demonstrate a record operational lifetime, with a half-lifetime of over 250 h at an initial luminance of 100 cd m-2.

18.
ACS Appl Mater Interfaces ; 11(2): 2103-2111, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30543281

RESUMO

Metal oxides as electrode materials are of great potential for rechargeable aqueous batteries. However, they suffer from inferior cycle stability and rate capability because of poor electronic and ionic conductivities. Herein, taking vertically orientated Bi2O3 nanoflakes on Ti substrates as examples, we find that the δ-Bi2O3 electrode with plenty of positively charged oxygen defects show remarkably higher specific capacity (264 mA h g-1) and far superior rate capability than that of α-Bi2O3 with less oxygen vacancies. Through pinpointing the existence form and the role of oxygen vacancies within the electrochemical processes, we demonstrate that oxygen vacancies in δ-Bi2O3 can not only promote electrical conductivity but also serve as central entrepots collecting OH- groups via electrostatic force effect, which has boosted the oxidation reaction and enhanced the electrochemical properties. Our work merits an excellent Bi2O3 negative electrode material via giving full play to the role of oxygen vacancies in electrochemical energy storage.

19.
ChemSusChem ; 12(5): 1000-1010, 2019 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-30565883

RESUMO

Ni/CeO2 enables either methane decomposition or water electrolysis for pure hydrogen production. Ni/CeO2 , prepared by a sol-gel method with only one heat treatment step, was used to catalyze methane decomposition for the generation of H2 . The solid byproduct, Ni/CeO2 /carbon nanotube (CNT), was further employed as an electrocatalyst in the hydrogen evolution reaction (HER) for H2 production. The Ni/CeO2 catalyst exhibits excellent activity for methane decomposition because CeO2 prevents carbon encapsulation of Ni nanoparticles during the preparation process and forms a special metal-support interface with Ni. The derived CNTs act as antenna to improve conductivity and promote the dispersion of agglomerated Ni/CeO2 . In addition, they provide H2 diffusion paths and prevent Ni/CeO2 from peeling off the HER electrode. Although long-term methane decomposition reduces the HER activity of Ni/CeO2 /CNTs (owing to degradation of the delicate Ni/CeO2 interface), the tunable nature of the synthesis makes this an attractive sustainable approach to synthesize future high-performance materials.

20.
ACS Energy Lett ; 3(7): 1571-1577, 2018 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-30505950

RESUMO

Lead halide perovskite nanocrystals are currently under intense investigation as components of solution-processed light-emitting devices (LEDs). We demonstrate LEDs based on Ag doped-passivated CsPbI3 perovskite nanocrystals with external quantum efficiency of 11.2% and an improved stability. Ag and trilayer MoO3/Au/MoO3 structure were used as cathode and anode, respectively, which reduce the electron injection barrier and ensure the high transparency and low resistance of the anode. Silver ions diffuse into perovskite film from the Ag electrode, as confirmed by the elemental mapping, the presence of Ag 3d peaks in the X-ray photoelectron spectrum, and the peak shift in the X-ray diffraction patterns of CsPbI3. In addition to doping, silver ions play the beneficial role of passivating surface defect states of CsPbI3 nanocrystals, which results in increased photoluminescence quantum yield, elongated emission lifetime, and improved stability of perovskite films.

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