ACS Applied Materials & Interfaces

Published by American Chemical Society
Online ISSN: 1944-8252
Publications
(a) Digital photograph of the gray-white as-electrospun PVA/(Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O composite fiber mats. (b) DSC−TGA (TA, SDT Q600) curves of the as-electrospun PVA/(Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O composite fibers. The heating rate is at 10 K min −1 under a static ambient atmosphere. Inset: Low-magnification SEM images of the as-electrospun (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O fibers. (c) Digital photograph of the greenish ascalcined (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NB mats. (d) Typical SEM image of the as-calcined (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NBs. Inset: SEM image with higher magnification.
(a) Typical bright-field and (b) dark-field TEM images of the as-calcined (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NBs, showing tiny nanograins. Inset in part b: SAED pattern indicating a nanoscale polycrystalline structure. Numbers on the ring pattern correspond to the 100 (1), 101 or 110 (2), 002 (3), 102 or 201 (4), 112 (5), and 103 (6) planes. (c) HRTEM (FEI TECNAI G 2 F20, 200 kV) image of the as-calcined (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NBs. (d) EDX mappings of Cu (upper left and right) and Zn (lower left and right). (e) Typical EDX spectrum of a single (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NB. Peaks corresponding to Zn, O, and Cu are evident. Mo signals are from a Mo TEM grid supporting the NWs. The specimens for HRTEM analysis were prepared by dissolving the black powder in ethanol. After ultrasonic treatment, a drop of the liquid was sprayed onto a holey-C Mo grid in order to avoid confusion with the Cu dopant.
(a) PXRD (The PANalytical Empyrean Series 2 diffraction system) data on a logarithmic scale for the y axis of the as-calcined (Cu 2 + / Cu 1 2+ ) 0.044 Zn 0.956 O NBs and (b) Williamson−Hall plot of the as-calcined (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NBs. (c) Raman spectrum [Jobin Yvon HR-800 spectrometer (resolution of 1 cm −1 )] of the as-calcined (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NBs. The experiments were carried out in a micro-Raman 180° backscattering geometry with 514.5 nm radiation from a 5 mW argon-ion laser at room temperature. The peak fittings were fit using an 80% Lorentzian−20% Guassian function. (d) Room temperature PL spectrum of the as-calcined (Cu 2 + /Cu 1 2+ ) 0.044 Zn 0.956 O NBs. The excitation wavelength is 325 nm from a helium−cadmium laser. Insets: digital photographs of the pure as-calcined ZnO NWs (top) and the as-calcined (Cu 2 + / Cu 1 2+ ) 0.044 Zn 0.956 O NBs (bottom) subjected to laser UV irradiation. The white arrows guide the eyes, and the white spot is the laser spot.
Temperature-dependent EPR spectra of the (Cu 2 + / Cu 1 2+ ) 0.044 Zn 0.956 O NBs. In the experiment, a Bruker ESRA-300 spectrometer operating at 9.4415 GHz (X band) between 100 K and room temperature (295 K) was used to take EPR data of the samples in a quartz capillary tube. Temperature control was maintained with a Bruker N2 temperature controller with a temperature error bar of ±1 K. The g factor can be calculated by the equation g = hν/μ B B, and the g values are shown.
(a) Possible Cu 2+ −V O (accurately Cu 2+ −V O + or further Cu 2+ ion−F center complexes) pair forms, where V O + denotes a V O capturing one electron, resulting from p−d hybridization between 3d band of Cu and O p bands (accurately V O p bands). F c and C represents the F center and the Cu 2+ ion−F c complex, respectively. (b) Schematic showing the Cu doping ZnO induced from the ferromagnetism-to-ferrimagnetism crossover.
Article
Unlike to the most previous reports, mixed Cu1+/Cu2+ cations doping-induced novel nanoscale phenomena including photoluminescence quenching, and a correlating ferrimagnetism with Néel temperature ≈ 14 K, were found in the as-calcined (Cu21+/Cu12+)0.044Zn0.956O electrospun nanobelts (NBs). There is also a high strain (up to 1.98 %), and a shrunk lattice distortion (△V/V0 ~ 0.127 %) in the (Cu21+/Cu12+)0.044Zn0.956O NBs, leading to lattice symmetry broken in conjunction with non-stoichiometry (i.e., oxygen vacancies or accurately F-centers), which could be as possible origins of ferrimagnetism in the Cu doped ZnO NBs. Electron paramagnetic resonance spectra reveals there are the giant and anisotropic g factors, suggesting that there is strong anisotropic spin-orbit interaction between Cu2+ ion and F-center (i.e. forming Cu2+ ─ F+ complexes) in the (Cu21+/Cu12+)0.044Zn0.956O NBs. The above correlation enables the potential applications of tuning the optical and ferrimagnetic properties through strain and F-centers engineering.
 
Article
Donor doped perovskite-type SrTiO3 experiences stoichiometry changes at high temperatures in different Po2 involving formation of Sr or Ti-rich impurities. NiO is incorporated into the stoichiometric strontium titanate, SrTi0.8Nb0.2O3-δ (STN), to form an A-site deficient perovskite material, (NiO)0.05-(SrTi0.8Nb0.2O3)0.95 (Ni-STN), for balancing the phase transition. Metallic Ni nano particles can be released upon reduction instead of forming undesired secondary phases. This material design introduces a simple catalytic modification method with good compositional control of the ceramic backbones, by which transport property and durability of solid oxide fuel cell anodes are largely determined. Using Ni-STN as anodes for solid oxide fuel cells, enhanced catalytic activity and remarkable stability in redox cycling have been achieved. Electrolyte-supported cells with the cell configuration of Ni-STN-SDC anode, LSGM electrolyte and LSCF cathode produce peak power densities of 612, 794, and 922 mW cm-2 at 800, 850 and 900oC, respectively, using H2 as the fuel and air as the oxidant. Minor degradation in fuel cell performance resulted from redox cycling can be recovered upon operating the fuel cells in H2. Such property makes Ni-STN a promising regenerative anode candidate for solid oxide fuel cells.
 
Article
Selective oxygen separation from air was carried out using ceramic membranes composed of Ba(0.95)La(0.05)FeO(3-δ). We demonstrated that surface abrasion of Ba(0.95)La(0.05)FeO(3-δ) membranes led to a significant increase in oxygen permeation fluxes at 700-930 °C because of an increase in surface reaction sites. Abrasion of the oxygen desorption side of the membrane resulted in a higher oxygen permeability than with abrasion on the oxygen sorption side. Moreover, an increase in the area of the oxygen desorption side also increased the oxygen permeability. The results suggest that oxygen permeation through Ba(0.95)La(0.05)FeO(3-δ) membranes is limited by the desorption of oxygen (surface reaction) and bulk diffusion. Attachment of a porous layer made of Ba(0.95)La(0.05)FeO(3-δ) to the membrane surface was also effective in increasing oxygen permeability. For example, a high permeation flux of 3.2 cm(3) min(-1) cm(-2) was achieved at 930 °C under a He/air gradient for a membrane (0.5 mm thickness) coated with a porous layer (14.4 μm).
 
Article
Perovskite Sr1-xCexCoO3-δ (0.05x0.15) have been prepared by a sol-gel method and studied as cathodes for intermediate temperature solid oxide fuel cells. As SOFC cathodes, Sr1-xCexCoO3- materials have sufficiently high electronic conductivities and excellent chemical compatibility with SDC electrolyte. The peak power density of cells with Sr0.95Ce0.05CoO3-δ is 0.625 W cm-2 at 700 oC. By forming a composite cathode with oxygen ion conductor SDC, the peak power density of the cell with Sr0.95Ce0.05CoO3-δ-30wt.%SDC composite cathode, reaches 1.01 W cm-2 at 700 oC, better than that of Sm0.5Sr0.5CoO3-based cathode. All these results demonstrates that Sr1-xCexCoO3-δ (0.05x0.15)-based materials are promising cathodes for an IT-SOFC.
 
Article
This paper presents a simple and effective oil-water interfacial self-assembly strategy to fabricate monolayer and bilayer nanofilms of densely packed Gd2O3:0.05X3+ (X = Eu, Tb) nanorods with characteristic luminescence properties. In this process, Gd2O3:0.05X3+ (X = Eu, Tb) nanotubes synthesized by a hydrothermal method are dispersed in deionized water, then a certain amount of n-hexane is added to produce a hexane-water interface. With n-butanol added as initiator, the nanotubes are gradually trapped at the interface to form a densely packed nanofilm. A monolayer nanofilm of densely packed Gd2O3:0.05Eu3+ nanorods is obtained after annealing. In addition, the bilayer nanofilm composed of Gd2O3:0.05X3+ (X = Eu, Tb) nanorods still retains the luminescence properties of each monolayer nanofilms. Moreover, the adhesion of the film on the substrate is very strong, which is extremely beneficial for its future applications.
 
Article
A mixture of two piezochromic compounds can be used as a universal shock detector, i.e., to determine the shock pressure without knowing a priori the temperature at which the shock occurred. For this purpose, both piezochromic compounds must exhibit different temperature influences in their transition-pressure values. This demonstration uses two piezochromic compounds (CoMoO4 and CuMoO4-type oxides) that exhibit a first-order phase transition between their two allotropic forms associated with a drastic color change. The colorimetric coordinates of the mixture indicate the pressure and temperature of a shock.
 
Article
Au nanocages synthesized from Ag nanocubes via the galvanic replacement reaction are finding widespread use in a range of applications because of their tunable optical properties. Most of these applications require the use of nanocages with a uniform size and in large quantities. This requirement translates into a demand for scaling up the production of Ag nanocubes with uniform, well-controlled sizes. Here we report such a method based on the modification of NaHS-mediated polyol synthesis with argon protection for fast reduction, which allows for the production of Ag nanocubes on a scale of 0.1 g per batch. The Ag nanocubes had an edge length tunable from 25 to 45 nm together with a size variation within +/-5 nm. The use of argon protection was the key to the success of this scale-up synthesis, suggesting the importance of controlling oxidative etching during synthesis.
 
Article
Layered Li-rich, Fe and Mn-based cathode material, Li[Li0.2Fe0.1Ni0.15Mn0.55]O2, has been successfully synthesized by a coprecipitation method and further modified with different coating amounts of AlPO4 (3wt.%, 5wt.% and 7wt.%). The effects of AlPO4 coating on the structure, morphology and electrochemical properties of these materials are investigated systematically. XRD results show that the pristine sample is obtained with typical Li-rich layered structure and trace amount of Li3PO4 phase are observed for the coated samples. The morphology observations reveal that all the samples show spherical particles (3-4 µm in diameter) with hierarchical structure, composed of nanoplates and nanoparticles. XPS analysis confirms the existence of AlPO4 and Li3PO4 phases at the surface. The electrochemical performance results indicate that the sample coated with 5wt.% AlPO4 exhibits the highest reversible capacity (220.4 mA h g-1 after 50 cycles at 0.1C), best cycling performance (capacity retention of 74.4% after 50 cycles at 0.1C) and rate capability (175.3 mA h g-1 at 1C, and 120.2 mA h g-1 at 10C after 100 cycles) among all the samples. Cycle voltammograms show good reversibility of the coated samples. EIS analysis reveals that charge transfer resistance after coating is much lower than that of the pristine sample. The excellent electrochemical performances can be attributed to the effects of multifunctional AlPO4 coating layer, including the suppression of surface side reaction and oxygen vacancies diffusion, the acceleration of lithium ions transport as well as the lower electrochemical resistance. Our research provides a new insight of surface modification on low-cost Li-rich material to achieve high energy as the next generation cathode of lithium-ion batteries.
 
Article
Morphology-controlled synthesis of tantalates is a major challenge in the field of material science. Herein, an innovative strategy has been developed for controllably synthesizing K1.9Na0.1Ta2O6•2H2O (KNTO) nanocrystals shaped as octahedra and nanosheets without using any capping agents. The obtained nanocrystals show high activity in photocatalytic H2 evolution from CH3OH/H2O solution, and their performance closely depends on the exposed facets, in which the {111}-facet-bounded nanooctahedra exhibit more than 3 times higher activity than the nanosheets dominated with {101} facets. The influence of surface atomic structure and electronic band structure on the photocatalytic properties of the KNTO nanocrystals is systematically studied. This is the first report for the facet controllable synthesis of tantalate materials with highly regular shapes. The present approach is anticipated as a general strategy for controllable synthesis of tantalate materials, and also provides feasibility for rational design and activity optimization of shape-controlled photocatalysts for H2 production.
 
Article
The dense ceramic membranes BaCo(0.7)Fe(0.2)Nb(0.1)O(3-δ) (BCFN) combined with GdBaCo(2-x)Fe(x)O(5+δ) (0 ≤ x ≤ 2.0) surface modification layers was investigated for hydrogen production by partial oxidation reforming of coke oven gas (COG). As oxygen permeation of BCFN membrane is controlled by the rate surface exchange kinetics, the GdBaCo(2-x)Fe(x)O(5+δ) materials improve the oxygen permeation flux of the BCFN membrane by 20-44% under helium atmosphere at 750 °C. The maximum oxygen permeation flux reached 14.4 mL min(-1) cm(-2) in the GdBaCoFeO(5+δ) coated BCFN membrane reactor at 850 °C, and a CH(4) conversion of 94.9%, a H(2) selectivity of 88.9%, and a CO selectivity of 99.6% have been achieved. The GdBaCo(2-x)Fe(x)O(5+δ) coating materials possess uniform porous structure, fast oxygen desorption rate and good compatibility with the membrane, which showed a potential application for the surface modification of the membrane reactor.
 
Article
As the most promising cathodes of lithium-ion batteries, lithium-rich manganese-based layered oxides with high capacity suffer from poor cycle stability, poor rate capability and fast voltage fading. Here we introduced AlF3 into the surface of layered lithium-rich cathode (Li[Li0.2Fe0.1Ni0.15Mn0.55]O2) as an artificial protective layer as well as an inducer of integrated layered-spinel structures to achieve both low cost and high capacity. The reduced irreversible capacity loss, improved cycling stability, and superior high-rate capability were ascribed to the combination of AlF3 nano coating and the unique structures as well as the low charge transfer resistance. Besides, the intractable issue, fast voltage fading of layered lithium-rich cathode, was also alleviated. Such materials with both low cost and high capacity are considered to be promising candidate cathodes to achieve lithium-ion batteries with high energy and high power.
 
Article
Al:HfO2 is grown on III-V compound substrates by atomic layer deposition after an in-situ trimethylaluminum-based preconditioning treatment of the III-V surface. After post-deposition rapid thermal annealing at 700°C, the cubic/tetragonal crystalline phase is stabilized and the chemical composition of the stack is preserved. The observed structural evolution of Al:HfO2 on pre-conditioned III-V substrates shows that the in-diffusion of semiconductor species from the substrate through the oxide is inhibited. Al-induced stabilization of Al:HfO2 crystal polymorphs up to 700°C can be used as a permittivity booster methodology with possibly important implications in the stack scaling issues of high-mobility III-V based logic applications.Abstract length is one paragraph.
 
Article
Conventional Ni-BaCeO3-based membranes possess high hydrogen permeation flux but suffer serious flux degradation in CO2-containing atmosphere due to the formation of BaCO3 insulating layer. In this work, we report a novel Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (Ni-BZCYYb) membrane, capable of both high hydrogen permeation flux and stable performance in CO2-containing atmosphere at 900 oC. Most importantly, the flux is found to be promoted rather than being diminished by CO2 normally observed for other high temperature proton conductors. The flux enhancement in Ni-BZCYYb membrane is attributed to the increase of moisture content in feed gas. When CO2 is introduced, the reverse water-gas shift reaction takes place generating H2O and CO. This work demonstrates that CO2 can be beneficial rather than detrimental for hydrogen permeation membranes that possess high chemical stability.
 
Article
Novel strategies based on spray-pyrolysis deposition are proposed to increase the triple-phase boundary (TPB) of La0.8Sr0.2MnO3- (LSM) cathodes in contact with yttria-stabilized zirconia (YSZ) electrolyte: i) nanocrystalline LSM films deposited on as-prepared YSZ surface; ii) the addition of polymethyl methacrylate microspheres as pore formers to further increase the porosity of the film cathodes; and (iii) the deposition of LSM by spray-pyrolysis on backbones of Zr0.84Y0.16O1.92 (YSZ), Ce0.9Gd0.1O1.95 (CGO) and Bi1.5Y0.5O3- (BYO) previously fixed onto the YSZ. This last method is an alternative to the classical infiltration process with several advantages for large-scale manufacturing of planar SOFCs, including easier industrial implementation, shorter preparation time and low cost. The morphology and electrochemical performance of the electrodes are investigated by scanning electron microscopy and impedance spectroscopy. Very low values of area specific resistance are obtained, ranging from 1.4 cm2 for LSM films deposited on as-prepared YSZ surface to 0.06 cm2 for LSM deposited onto BYO backbone at a measured temperature of 650 ºC. These electrodes exhibit high performance even after annealing at 950 ºC, making them potentially suitable for applications in SOFCs at intermediate temperatures.
 
Article
In this study, Ni/BaCe0.75Y0.25O3-δ (Ni/BCY25) was investigated as an anode for direct ammonia-fueled solid oxide fuel cells. The catalytic activity of Ni/BCY25 for ammonia decomposition was found to be remarkably higher than Ni/8 mol % Y2O3-ZrO2 and Ni/Ce0.90Gd0.10O1.95. The poisoning effect of water and hydrogen on ammonia decomposition reaction over Ni/BCY25 was evaluated. In addition, an electrolyte-supported SOFC employing BaCe0.90Y0.10O3-δ (BCY10) electrolyte and Ni/BCY25 anode was fabricated, and its electrochemical performance was investigated at 550-650 °C with supply of ammonia and hydrogen fuel gases. The effect of water content in anode gas on the cell performance was also studied. Based on these results, it was concluded that Ni/BCY25 was a promising anode for direct ammonia-fueled SOFCs. An anode-supported single cell denoted as Ni/BCY25|BCY10|Sm0.5Sr0.5CoO3-δ was also fabricated, and maximum powder density of 216 and 165 mW cm(-2) was achieved at 650 and 600 °C, for ammonia fuel, respectively.
 
(a) X-ray diffraction θ−2θ scan of the 100 nm BFGO thin film grown on the LNO-buffered NCAO (001) pc substrate. Reciprocal space mappings around diffraction spots (b) (-1-18) and (c) (0-19) of the NCAO substrate, along with BFGO (-1-13) and (0-13), respectively.  
Relative Energies of All Tetragonal and Rhombohedral Structures with Different Configurations of Fe/Ga Atoms and Spin Orderings of Fe Atoms a 
(a) Low magnification cross-sectional TEM image of BFGO/LNO/NCAO heterostructure with an inset showing the enlarged image of the boundary-like region. (b) SAED pattern taken along [-110] zone axis, where the split of BFGO (221) spots is indicated by the white circle. (c) High resolution TEM image of the BFGO super-tetragonal-like structure.  
Schematics showing (a) the BFGO unit cell and (b) the configuration of four twinning variants. The reciprocal relationships between real lattice and reciprocal lattice for (c) (HHL) mapping and (d) (H0L) mapping.  
Article
Ferroelectric perovskites with strongly elongated unit cells (c/a > 1.2) are of particular interest for realizing giant polarization induced by significant ionic off-center displacements. Here we show that epitaxial BiFe0.6Ga0.4O3 (BFGO) thin films exhibit a stable super-tetragonal-like structure with twinning domains regardless of film thickness and substrate induced strain, evidenced with high resolution X-ray diffractometry (HR-XRD), transmission electron microscopy (TEM) and Piezoresponse force microscopy (PFM).The origin of the structural stability of BFGO is investigated by the first-principles calculation. The ferroelectric properties of BFGO are studied by PFM, first-principles calculation and macroscopic polarization-electric field (P-E) hysteresis measurement. A giant ferroelectric polarization of ~150 μC/cm(2) is revealed by the first-principles calculations and confirmed by experiments. Our studies provide an alternative pathway of employing Ga-substitution other than the extensively studied strain engineering to stabilize the super-tetragonal structure in BiFeO3-based epitaxial thin films.
 
Article
The effects of Pt and RuO2 top electrodes on the electrical properties of capacitors with Al-doped TiO2 (ATO) films grown on the RuO2 bottom electrode by an atomic layer deposition method were examined. The rutile phase ATO films with high bulk dielectric constant (> 80) were well grown due to the local epitaxial relationship with the rutile structured RuO2 bottom electrode. However, the interface between top electrode and ATO was damaged during the sputtering process of the top electrode, resulting in the decrease in the dielectric constant. Post-metallization annealing at 400 oC was performed to mitigate the sputtering damage. During the post-metallization annealing, the ATO layer near the RuO2 top electrode/ATO interface was well-crystallized because of the structural compatibility between RuO2 and rutile ATO, while the ATO layer near the Pt top electrode/ATO interface still exhibited an amorphous-like structure. Despite the same thickness of the ATO films, therefore, the capacitors with RuO2 top electrodes showed higher capacitance compared to the capacitors with Pt top electrodes. Eventually, an extremely low equivalent oxide thickness of 0.37 nm with low enough leakage current density (<10-7 A/cm2 at 0.8 V) and physical thickness of 8.7 nm for the next-generation dynamic random access memory was achieved from ATO films with RuO2 top electrodes.
 
Article
Hierarchical micro/nano-structured MnO material is synthesized from a precursor of MnCO3 with olive shape that is obtained through a facile one-pot hydrothermal procedure. The hierarchical micro/nano-structured MnO is served as anode of lithium ion battery together with a cathode of spinel LiNi0.5Mn1.5O4-δ material, which is synthesized also from the precursor of MnCO3 with olive shape through a different calcination process. The structures and compositions of the as-prepared materials are characterized by TGA, XRD, BET, SEM and TEM. Electrochemical tests of the MnO materials demonstrate that it exhibit excellent lithium storage property. The MnO material in a MnO / Li half cell can deliver a reversible capacity of 782.8 mAh g-1 after 200 cycles at a rate of 0.13 C, and a stable discharge capacity of 350 mAh g-1 at a high rate of 2.08 C. Based on the outstanding electrochemical property of the MnO material and the LiNi0.5Mn1.5O4-δ as well, the MnO / LiNi0.5Mn1.5O4-δ full cell has demonstrated a high discharge specific energy ca. 350 Wh kg-1 after 30 cycles at 0.1 C with an average high working voltage at 3.5 V and a long cycle stability. It can release a discharge specific energy of 227 Wh kg-1 after 300 cycles at a higher rate of 0.5 C. Even at a much higher rate of 20 C, the MnO / LiNi0.5Mn1.5O4-δ full cell can still deliver a discharge specific energy of 145.5 Wh kg-1. The excellent lithium storage property of the MnO material and its high performance as anode in the MnO / LiNi0.5Mn1.5O4-δ lithium ion battery is mainly attributed to its hierarchical micro/nano-structure, which could buffer the volume change and shorten the diffusion length of Li+ during the charge/discharge processes.
 
Article
A series of O3-phase NaFex(Ni0.5Mn0.5)1-xO2 (x=0, 0.1, 0.2, 0.3, 0.4 and 1) samples with different Fe contents was prepared and investigated as high-capacity cathodic hosts of Na ion batteries. The partial substitution of Ni and Mn with Fe in the O3-phase lattice can improve greatly the electrochemical performance and the structural stability. It is found that the NaFe0.2Mn0.4Ni0.4O2 cathode with the optimized Fe content of x=0.2 can deliver an initial reversible capacity of 131 mAh g-1, a reversible capacity of >95% over 30 cycles and a high rate capacity of 86 mAh g-1 at 10 C at a voltage range of 2.0 ~ 4.0 V. The structural characterizations reveal that pristine NaMn0.5Ni0.5O2 and Fe-substituted NaFe0.2Mn0.4Ni0.4O2 lattices underwent different phase transformations from P3 to P3'' and from P3 to OP2 phases respectively at high voltage interval. The as-resulted OP2 phase by Fe substitution has smaller interslab distance (5.13 Å) than the P3'' phase (5.74 Å), which suppresses the co-insertion of the solvent molecules and/or electrolyte anions and therefore enhances the cycling stability in the high voltage charge. This finding suggests a new strategy for creating cycle-stable transition-metal oxide cathodes for high-performance Na-ion batteries.
 
Article
As the molecular precursor of ZnSe, ZnSe∙0.5(N2H4) inorganic-organic hybrids have received relatively less attention due to the feasibility of their further processing and decomposition into pure-phase ZnSe. Here we demonstrated that ZnSe∙0.5(N2H4) hybrid nanostructures, which were prepared using a facile hydrazine-assisted hydrothermal method, may practically harvest solar energy for photoconversion applications. By modulating the volume ratio of hydrazine hydrate to deionized water employed in the synthesis, the morphology of the grown ZnSe∙0.5(N2H4) can be varied, which included nanowires, nanobelts and nanoflakes. With the relatively long exciton lifetime and highly anisotropic structure, ZnSe∙0.5(N2H4) nanowires performed much better in the photodegradation of rhodamine B than the other two counterpart products. As compared to pure ZnSe nanoparticles and single-phase ZnSe nanowires obtained from further processing ZnSe∙0.5(N2H4), the ZnSe∙0.5(N2H4) hybrid nanowires exhibited superior photocatalytic performance under visible light illumination. The hybrid nanowires were further decorated with Au particles to endow them with structural and compositional diversities. Time-resolved photoluminescence spectra suggested that almost 40 % of the photoexcited electrons in ZnSe∙0.5(N2H4) nanowires can be transported to the decorated Au, which enabled a fuller extent of participation of charge carriers in the photocatalytic process and thus conduced to a significant enhancement in the photocatalytic activity. The demonstrations from this work illustrate that ZnSe∙0.5(N2H4) hybrid nanostructures can serve as a versatile photocatalyst platform for advanced photocatalytic applications.
 
Article
Mesoporous Ni0.85Se nanospheres have been synthesized on graphene via hydrothermal approach. Due to the exceptional electron-transfer pathway of graphene and the excellent catalytic ability of the mesoporous Ni0.85Se nanospheres, the nanocomposites exhibited excellent electrocatalytic property as the counter electrode (CE) of dye-sensitized solar cells (DSSCs). The more catalytic active sites, higher catalytic activity, and better charge-transfer ability of Ni0.85Se@RGO CE lead to faster and more complete reaction of the I3-. The Ni0.85Se@RGO reached high power conversion efficiency (PCE) of 7.82%, which is better than the photovoltaic performance of the DSSC using a Pt CE (7.54%). EIS, CV, and Tafel polarization have been carried out to demonstrate higher catalytic activity and more outstanding charge-transfer ability of Ni0.85Se@RGO than Pt.
 
Article
To increase the open-circuit voltage (Voc) of dye-sensitized solar cells (DSCs) is crucial to enhance the photovoltaic efficiency of DSCs. Here, we report an effective method to significantly improve the Voc and photovoltaic efficiency of DSCs by using gel-coated composites of reduced graphene oxide (rGO) and single-walled carbon nanotubes (SWCNTs) as the counter electrode. Gel-coated rGO-SWCNT composites outperform Pt, rGO and SWCNTs in catalyzing the reduction of I3- and functioning as the counter electrode of DSCs. The Voc and power conversion efficiency (PCE) are 0.86 V and 8.37% for fresh DSCs with the composite of 80 wt% rGO and 20 wt% SWCNTs, significantly higher than those (Voc = 0.77 V, PCE = 7.79%) of control DSCs with Pt fabricated by pyrolysis as the counter electrode. The Voc value of DSCs with rGO/SWCNT composites as the counter electrode further increases to 0.90 V after one week. The high Voc and PCE are ascribed to the synergetic effects of rGO and SWCNTs in reducing the overpotential of the I3- reduction. RGO with high specific surface area can have high electrocatalytic activity, whereas SWCNTs give rise to high conductivity for the composites and facilitate the penetration of the redox species into rGO sheets by preventing the agglomeration of the rGO sheets. To the best of our knowledge, this is the first time to report iodide/triiodide DSCs with both high Voc and PCE.
 
Article
Highly elongated BiFeO3 are epitaxially grown on hexagonal sapphire(0001) substrates within a rather narrow synthesis window. Both x-ray reciprocal space maps and Raman characterizations reveal that it is of true tetragonal symmetry but not the commonly observed MC type monoclinic structure. The tetragonal BiFeO3 film exhibits an island growth mode with the island edges oriented parallel to the <10-10> and <12-30> directions of the sapphire substrate. With increasing the deposition time a transition from square island to elongated island and then to a continuous film is observed. The metastable tetragonal phase can retain on the substrate without relaxation to the thermally stable rhombohedral phase up to a critical thickness of 450 nm, providing an exciting opportunity for practicable lead-free ferroelectrics. These results facilitate a better understanding on the phase stability of BiFeO3 polymorphs, and enrich the knowledge about the heteroepitaxial growth mechanism of functional oxides on symmetry-mismatched substrates.
 
Article
One dimensional zigzag GaN nanorods with corrugated morphology have been synthesized on graphite substrate for the first time without the assistance of any metal catalyst through a feasible thermal evaporation process. The morphologies and microstructures of GaN nanorods were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results from HRTEM analysis indicate that the GaN nanorods are well crystallized and exhibit a preferential orientation along the [0001] direction with Ga-terminated (101 ̅1 ̅) and N-terminated (101 ̅1) as side facets, finally leading to the corrugated morphology surface. The stabilizing of the electrostatic surface energy of {101 ̅1} polar surface in a wurtzite-type hexagonal structure plays a key role in the formation of GaN nanorods. Room-temperature cathodoluminescence (CL) measurements showed that a near-band-edge (NBE) emission in the ultraviolet range and a broad deep level emission (DLE) in visible range are observed under electron beam irradiation. The crystallography and the optical emissions of GaN nanorods are discussed.
 
Article
A basic understanding of the affinity between the hydroxyapatite (HA) and α-Ti surfaces is obtained through electronic structure calculations by first-principles method. The surface energies of HA(0001), HA , HA , and Ti(0001) surfaces have been calculated. The HA(0001) presents the most thermodynamically stable of HA. The HA/Ti interfaces were constructed by two kinds of interface models, the single interface (denoted as SI) and the double-interface (denoted as DI). Two methods, the full relaxation and the UBER, were applied to determine the interfacial separation and the atomic arrangement in the interfacial zone. The works of adhesion of interfaces with various stoichiometric HA surfaces were evaluated. For the HA(0001)/Ti(0001) interfaces, the work of adhesion is strongly depended on the chemical environment of the HA surface. The values are -2.33, -1.52, and -0.80 J/m2 for the none-, single-, and double-Ca terminated HA/Ti interfaces, respectively. The influence of atomic relaxation on the work of adhesion and interface separation is discussed. Full relaxation results -1.99 J/m2 work of adhesion and 0.220 nm separation between HA and Ti for the DI of 1-Ca-HA/Ti interface, while they are -1.14 J/m2 and 0.235 nm by partial relaxation. Analysis of electronic structure reveals that charge transfer between HA and Ti slabs occurs during the formation of the HA/Ti interface. The transfer generates the Ti-O or Ti-Ca bonds across the interface and drives the HA/Ti interface system to metallic characteristic. The energetically favorable interfaces are formed when the outmost layer of HA comprises more O atoms at the interface.
 
Article
Silicene consists of a monolayer of Si atoms in a buckled honeycomb structure and is expected to be well compatible with the current Si-based technology. However, the band gap is strongly influenced by the substrate. In this context, the structural and electronic properties of silicene on MgBr2(0001) modified by Li and Na are investigated by first-principles calculations. Charge transfer from silicene (substrate) to substrate (silicene) is found for substitutional doping (intercalation). As compared to a band gap of 0.01 eV on the pristine substrate, strongly enhanced band gaps of 0.65 eV (substitutional doping) and 0.24 eV (intercalation) are achieved. The band gap increases with the dopant concentration.
 
Article
Photoelectrochemical solar fuel synthesis devices based on photoactive hematite (α-Fe2O3) anodes have been extensively investigated, yet a fundamental understanding regarding its associated water oxidation surface reaction mechanism is still lacking. To help elucidate detailed reaction mechanisms, we studied water chemisorption and reaction as well as structural changes induced by Ni incorporation into the α-Fe2O3(0001) surface. Investigation by scanning probe and electron diffraction techniques show that vapor deposition of Ni and subsequent annealing to 700 K leads to the interdiffusion and incorporation of Ni into the near-surface region of hematite and changes the structure of the (0001) surface by the formation of FeO-like domains on the topmost layer. These results are discussed in the context of a proposed water oxidation mechanism on this surface in which Ni doping facilitates water oxidation by increasing O hole concentrations and forms less negatively charged O anions (*O) and *O---OH species [P. L. Liao, J. A. Keith, E. A. Carter, J. Am. Chem. Soc. 2012, 134, 13296-13309.]. Consistent with predictions from this theory, electrochemical measurements using cyclic voltammetry carried out on the UHV-prepared surfaces demonstrated that Ni incorporation leads to higher current density and lower onset potential than the unmodified α-Fe2O3 surface. Our work utilizing a surface science approach helps to connect such theoretical predictions of reaction thermodynamics on well-defined structures and the performance of modified hematite model electrocatalysts for water oxidation.
 
Article
We have demonstrated nitrogen-polar (000-1) (N-polar) InGaN multiple quantum wells (MQWs) with significantly improved luminescence properties prepared by pulsed metalorganic chemical vapor deposition. During the growth of InGaN quantum wells, Ga and N sources are alternately injected into the reactor to alter the surface stoichiometry. The influence of flow duration in pulsed growth mode on the luminescence properties has been studied. We find that use of pulsed-mode creates high density of hexagonal mounds with increased InGaN growth rate and enhanced In composition around screw-type dislocations, resulting in remarkably improved luminescence properties. The mechanism of enhanced luminescence caused by hexagonal mounds has been discussed. Luminescence properties of N-polar InGaN MQWs grown with short pulse durations have been significantly improved in comparison with the sample grown by conventional continuous growth method.
 
Article
A TiO2 film with dominant anatase {001} facets is directly prepared by direct-current reactive magnetron sputtering at room temperature without using morphology-controlling agents. The formation mechanism of anatase TiO2 films with dominant {001} facets is explained by the competition between thermodynamics and ion impinging in the deposition process. The crystalline TiO2 film shows a superior photocatalytic efficiency for the degradation of Rhodamine B under UV-visible (λ > 250 nm) lights. Furthermore, a comparable photodegradation of Rhodamine B is also found on the TiO2 film surface by using visible (λ > 420 nm) lights. During film growth, the surface bombarded by high energy of ions yields plenty of oxygen defects, which can enhance the photocatalytic activity of the films irradiated under visible light.
 
Article
Ferromagnetic thin films of the A-site nano-ordered double perovskite LaBaCo(2)O(5.5+δ) (LBCO) were grown on (001) MgO, and their structural and magnetic properties were characterized. The as-grown films have an excellent epitaxial behavior with atomically sharp interfaces, with the c-axis of the LBCO structure lying in the film plane and the interface relationship given by (100)(LBCO)//(001)(MgO) and [001](LBCO)//[100](MgO) or [010](MgO). The as-grown LBCO films exhibit a giant magnetoresistance (54% at 40 K under 7 T) and an anomalous magnetic hysteresis, depending strongly on the temperature and the applied magnetic field scan width.
 
Article
Teeth-like homojunctions BiOCl (001) nanosheets with tunable photoresponse were constructed by selective etching with triethanolamine and allowed fast charge separation across the interfaces to facilitate photocatalysis. The unique microstructure exhibits a superior photocatalytic activity which can be ascribed to the combined interaction of the high UV/vis light harvest, high photogenerated charges separation efficiency, and the fast interfacial charge-transfer rate based on the unique homogeneous topotactic structure. We believe that the creation of this new model junction may be a great aid in the design and preparation of efficient semiconductor based photocatalysts and a new understanding of the essential relation between the junction and the photocatalytic activity.
 
Article
BiOCl is known as a highly efficient photocatalyst for degradation of pollutants. However, effective methods for fabricating BiOCl nanomaterials with well-defined facets are still lacking. In this work, a facile synthetic method was developed for the fabrication of BiOCl nanodisks with exposed {001} facets. The central feature of this approach was the use of water as the hydrolysis agent and ethylene glycol as the crystal growth inhibitor agent to tune the growth of BiOCl nanomaterial. With this approach, the size and shape of BiOCl nanostructures could be effectively tuned through adjusting the volume ratio of ethylene glycol/H2O. In addition, the mechanism of the crystal growth in this fabrication process was elucidated. The as-prepared BiOCl nanodisks with exposed {001} facets exhibited an excellent photocatalytic activity towards Rhodamine B degradation under both ultraviolet and visible light irradiations. These findings shed light on the deep understanding of formation mechanisms of BiOCl nanodisks and provide an efficient and facile method for the synthesis of high active photocatalyst.
 
Article
Polyaniline (PANI)-decorated {001} facets of Bi2O2CO3 nanosheets were synthesized by a low temperature chemical method. We demonstrate that the strong interfacial interactions between Bi2O2CO3 {001} facets and PANI could promote in situ formation of oxygen vacancy at the interface confirmed by both DFT calculations and electron spin resonance (ESR) experiments, which is due to the high oxygen density characteristic of Bi2O2CO3 {001} facets. In addition, such interfacial interaction also leads to a 0.38 eV positive shifting of the valance band (VB) of Bi2O2CO3. Importantly, the decorated PANI can stabilize these interfacial oxygen vacancies. Therefore, the migration and separation of photogenerated carriers have been improved significantly evidenced by electrochemical impedance spectroscopy (EIS), photoluminescence (PL) and ns-time-resolved fluorescence decay spectra, resulting in a 4.5 times higher activity toward photodegradation of Rhodamine B and a 6 times higher photocurrent density compared to their corresponding bare Bi2O2CO3. The finding of the in situ oxygen vacancy formation at the interface could provide some hints for the deep understanding of the interactions between PANI and crystal facets of semiconductors to develop high efficient photocatalysts.
 
Article
Varying the film thickness is a precise route to tune the interfacial strain to manipulate the properties of the multiferroic materials. Here, to explore the effects of the interfacial strain on the properties of the multiferroic BiFeO3 films, thickness-dependent structural and polarization evolutions of the BiFeO3 films were investigated. The epitaxial growth with an atomic stacking sequence of BiO/TiO2 at the interface was confirmed by scanning transmission electron microscopy. Combining x-ray diffraction experiments and first-principles calculations, a thickness-dependent structural evolution was observed from a fully strained tetragonality to partially relaxed one without any structural phase transition or rotated twins. The tetragonality (c/a) of the BiFeO3 films increases with decreasing the film thickness, while the polarization is in contrast with this trend, and the size effect including the depolarization field plays a crucial role in this contradiction in thinner films. These findings offer an alternative strategy to manipulate structural and polarization properties by tuning the interfacial strain in epitaxial multiferroic thin films.
 
Article
Understanding the contact-semiconductor interface is important in determining the performance of a semiconductor device. This study investigated the contact chemistry of BiI(3) single crystal with Au, Pd, and Pt electrodes using X-ray photoelectron spectroscopy (XPS), a technique widely used to probe the interfacial chemistry of many materials. Chemical reactions were identified on the BiI(3) surface for the case of Pd and Pt contacts, while Au showed no reactivity with BiI(3). The difference in reactivities correlated with different surface morphologies of the contact on the BiI(3) surface, which was evidenced by atomic force microscopy (AFM) characterization. The dark resistivity of the BiI(3) crystal with above contact materials was measured by I-V characterization. The highest resistivity was obtained when Au was employed as the contact. These results suggest that Au is better than Pd and Pt as the contact material for BiI(3) single crystal.
 
Article
The emerging two-dimensional electron gas (2DEG) at the interface between polar LaAlO3 (LAO) and nonpolar SrTiO3 (STO) provides potential applications in low-dimensional nanoelectronic devices because of its exceptional electron transport property. To form 2DEG in the LAO/STO heterostructure (HS), a minimum thickness of approximately 4 unit cells of LAO is necessary. Herein, we modeled the n-type (TiO2)(0)/(LaO)(+1) HS by depositing (LAO)n (n = 4, 5, and 6) thin films on the STO substrate and explored strain effects on the critical thickness for forming 2DEG in the LAO/STO HS-based slab systems using first-principles electronic structure calculations. A vacuum layer was added along the [001] direction on the LAO film to resemble the actual epitaxial growth process of the materials. An insulator-to-metal transition is predicted in unstrained (LAO)n/STO systems when n ≥ 5. Our calculations indicate that O 2px/py states give rise to the surface conductivity, while Ti 3dxy states are responsible for the interfacial conductivity. For the tensilely strained HS system, an increased film thickness of LAO (n ≥ 6) is required to form the 2DEG, and a remarkable shift of O 2p orbitals toward higher energy in LAO layers is found, which is caused by the strain-induced change of the electrostatic potential. For the compressively strained HS system, the critical thickness of LAO film for forming 2DEG is between 5 and 6 unit cells of LAO. In addition, our calculations suggest that the interfacial charge carrier density and magnetic moment can be optimized when a moderate tensile strain is applied on the STO substrate in the ab-plane.
 
Article
Hierarchical nanostructures have attracted increasing interest due to their exceptional properties and widespread potential applications. In this paper, anatase TiO2 hollow nanoboxes (TiO2-HNBs) are formed by assembly of nanosheets with exposed {001} facets by solvothermal treatment of TiOF2 cubes in alcohols (tert-butanol and ethanol) at 180 oC. It was found that phase transformation of TiOF2 to anatase TiO2 begins at corners and edges of TiOF2 cubes due to in situ hydrolysis of TiOF2, where water was produced by dehydration of alcohol molecules. With extension the reaction time, TiO2-HNBs assembly from nanosheets with exposed high-energy {001} facets were formed due to the steady inside-outside dissolution-recrystallization process. However, the resulted hierarchical TiO2-HNBs are unstable, which can decompose to discrete high-energy TiO2 nanosheets if further extension the reaction time. The hierarchical TiO2-HNBs show higher photocatalytic activity than discrete high-energy TiO2 nanosheets and P25 TiO2 due to the unique structures of TiO2-HNBs.
 
Article
We investigated the crystal growth of piperonyl (E,E)-muconate [bis(3,4-methylenedioxybenzyl) (E,E)-muconate, MDO] on inorganic crystalline substrates during vapor deposition for the control of polymer chain alignment by the subsequent solid-state photopolymerization of the MDO monomer thin films deposited on the substrate. We controlled the arrangement of the MDO molecules and the polymer chains produced on the substrate, depending on the lattice parameters of the substrate surfaces used. The epitaxial crystal growth of MDO on the {001} plane of a KCl single crystal was observed under the condition that the crystal lattice lengths of MDO agreed well with the specific space distance of the substrate; i.e., the KCl cubic crystal resulted in a d(110) value of 4.45 Å, which was very close to the value of the monomer stacking distance in the MDO crystal (d(s) = 4.43 Å). On the other hand, slightly large and too small d(110) values for KBr and NaCl, respectively, resulted in the less controlled and no epitaxial crystal growth of MDO. The irradiation of polarized UV light on the MDO thin-film crystal produced highly regulated polymer alignment in a specific direction on the KCl substrate.
 
Article
Highly epitaxial LaBaCo2O5.5+δ thin films were grown on the vicinal (001) SrTiO3 substrates with miscut angles of 0.5o, 3.0o and 5.0o to systemically study strain effect on its physical properties. The electronic transport properties and magnetic behaviors of these films are strongly dependent on the miscut angles. With increasing the miscut angle, the transport property of the film changes from semiconducting to semimetallic, which results most probably from the locally strained domain induced by the surface step terraces. In addition, a very large magnetoresistance (34% at 60 K) was achieved for the 0.5o-miscut film, which is about 30% larger than that for the film grown on the regular (001) SrTiO3 substrates.
 
Article
The magnetic structure of the interfaces between organic semiconductors and ferromagnetic contacts plays a key role in the spin injection and extraction processes in organic spintronic devices. We present a combined computational (density functional theory) and experimental (x-ray magnetic circular dichroism) study on the magnetic properties of interfaces between bcc-Fe(001) and C(60) molecules. C(60) is an interesting candidate for application in organic spintronics due to the absence of hydrogen atoms and the associated hyperfine fields. Adsorption of C(60) on Fe(001) reduces the magnetic moments on the top Fe layers by ≈6%, while inducing an anti-parrallel magnetic moment of ≈-0.2 μ(B) on C(60). Adsorption of C(60) on a model ferromagnetic substrate consisting of three Fe monolayers on W(001) leads to a different structure, but to very similar interface magnetic properties.
 
Article
Formaldehyde (HCHO), as the main indoor air pollutant, is highly needed to be removed by adsorption or catalytic oxidation from the indoor air. Herein, the F-, OH- and Cl--modified anatase TiO2 nanosheets (TNS) with exposed (001) facets were prepared by a simple hydrothermal and post-treatment method, and their HCHO adsorption performance and mechanism were investigated by the experimental analysis and theoretical simulations. Our results indicated that the adsorbed F-, OH- and Cl- ions all could weaken the interaction between HCHO and TNS surface, leading to the serious reduction of HCHO adsorption performance of TNS. However, different from F- and Cl- ions, OH- ion could induce the dissociative adsorption of HCHO by capturing one H atom from HCHO, resulting in the formation of one formyl group and one H2O-like group. This greatly reduced the total energy of HCHO adsorption system. Thus, the adsorbed OH- ions could provide the additional active centers for HCHO adsorption. As a result, the NaOH-treated TNS showed the best HCHO adsorption performance mainly because its surface F- was replaced OH-. This study will provide new insight into the design and fabrication of high performance adsorbents for removing indoor HCHO, also will enhance the understanding of HCHO adsorption mechanism.
 
Article
TiO2 films consisting of single-crystal anatase nanoparticles with exposed {001} facets were fabricated from anodized TiO2 nanotube arrays. The films' photocatalytic activities were further activated and then enhanced (∼2.5 times) by removing F(-) from the {001} facets. This study indicates that fluorine-free crystal surfaces are of great importance for the application of such kinds of single-crystal TiO2 nanoparticle films with exposed {001} facets in related areas.
 
Article
Anatase TiO2 nanosheets supported on reduced graphene oxide (RGO) were synthesized via a one-step, solvothermal method. During the solvothermal step, GO was reduced to RGO, and, subsequently, anatase TiO2 with 73.7% exposed {001} facets was grown in situ on the surfaces of the RGO nanosheets. Compared with pure TiO2, the RGO/TiO2 hybrid nanocomposite had improved photoactivity as a result of effective photoinduced electron transfer from TiO2 to the RGO acceptor through interfacial interactions. Trapping tests showed that the oxidation of dye molecules proceeded for about 22% through the reaction with •OH radicals, and the remaining 78% occurred via direct interactions with holes. The holes left in TiO2 crystals were the main reason for the enhanced photocatalytic properties of the RGO/TiO2 composite. This paper not only reports the fabrication of highly active photocatalysts but also gives deeper insights into the photocatalytic mechanism of carbon/TiO2 composites.
 
Article
A hydrothermal method was developed to grow ultrathin MoS2 nanosheets, with an expanded spacing of the (002) planes, on carbon nanotubes. When used as a sodium-ion battery anode, the composite exhibited a specific capacity of 495.9 mAh g-1, and 84.8% of the initial capacity was retained after 80 cycles, even at a current density of 200 mA g-1. X-ray diffraction analyses show that the sodiation/desodiation mechanismis based on a conversion reaction. The high capacity and long-term stability at a high current ate demonstrate that the composite is a very promising candidate for use as an anode material in sodium-ion batteries.
 
Article
{010}-facet exposed anatase TiO2 crystals exhibit the highest photoreactivity among the exposed facets. To obtain a higher exposure rate of this facet, the work investigated the transformation of the nanosheets with cavities within the layers, derived from the salt-rock structured Li2TiO3 precursor. All the lithium ions were extracted from the precursor by the H+/Li+ ion exchange in HCl aqueous solutions, and after tetramethylammonium ions were intercalated, the precursor can delaminated into the nanosheets. The [TiO3]2- nanosheets were hydrothermally treated under different temperatures and pH values. The results showed that the anatase phase was formed in a wider range of pH and temperature, comparing with using the nanoribbons of [Ti4O9]2- and the nanosheets of [Ti1.73O4]2-. At low pH, the [111]-faceted nanorod-shaped anatase nanocrystals were formed preferentially, and the nanocrystals preferentially growth along the [001] direction with the increase of pH of the solution, leading to a large percentage of {010} facets on their surface. The photocatalytic activity increases with the increase of exposure rate of {010} facets.
 
Article
As we know, Li+-ions transport in layered LiNi1/3Co1/3Mn1/3O2 (NCM) through a two-dimensional channel parallel to the Li+-ions layers which are indexed as {010} active planes. In this paper, NCM nanoplates with exposing {010} active facets are synthesized in a polyol medium (ethylene glycol) and characterized by XRD, XPS, SEM and HR-TEM. In addition, the effects of reaction conditions on the morphology, structure and electrochemical performance are also evaluated. The results show that the increased thickness of NCM nanoplates can enable more {010} facets exposed leading to more channels for Li+-ions migration. However, when the annealing temperatures exceed 900 ºC, many new crystal planes grow along the thickness direction covering the {010} facets. In all of the NCM nanoplates obtained at different conditions, the NCM nanoplates calcined at 850 ºC for 12h (NCM-850-12H) display a high initial discharge capacity of 207.6 mAh g-1 at 0.1 C (1 C = 200 mA g-1) between 2.5 and 4.5 V higher than most of NCM materials as cathodes for lithium ion batteries. The discharge capacities of NCM-850-12H are 169.8, 160.5 and 149.3 mAh g-1 at 2, 5 and 7 C, respectively, illustrating the excellent rate capability. The superior electrochemical performance of NCM-850-12H cathode can be attributed to more {010} active planes exposure.
 
Article
Li4Ti5O12/TiO2 hollow spheres composed of nanoflakes with preferentially exposed Li4Ti5O12 (011) facets have been successfully fabricated via a facile hydrothermal processing route and following calcination. These hollow spheres show good electrochemical performance in terms of high capacity (266 mAh g-1 at 0.1 A g-1), and excellent rate capability (110 mAh g-1 at 4.0 A g-1 up to 100 cycles), attributed to unique morphology, preferred facet orientation of the nanoflakes and microscopic structure of the hollow spheres. The preferentially exposed Li4Ti5O12 (011) facets leads to fast lithium insertion/deinsertion processes in materials because of shorten lithium ion diffusion length, proved to be highly effective in improving the electrochemical properties of the hollow spheres. The excellent electrochemical performance makes these hollow spheres promising anode material for lithium ion batteries with high power and energy densities.
 
Top-cited authors
C.P. Wong
  • Georgia Institute of Technology
Lei Jiang
  • Jilin University
Fei Xiao
  • Hunan University
Lingxin Chen
  • Chinese Academy of Sciences
Hongcai Gao
  • Beijing Institute of Technology