Ranbo Yu

α-Fe2O3 multi-shelled hollow microspheres for lithium ion battery anodes with superior capacity and charge retention

Multi-shelled α-Fe2O3 hollow microspheres were synthesized using carbonaceous microsphere sacrificial templates and utilized for high capacity anode materials in lithium ion batteries (LIBs). Structural aspects including the shell thickness, number of internal multi-shells, and shell porosity were controlled by synthesis parameters to produce hollow microspheres with maximum lithium capacity and stable cycling behavior. Thin, porous, hollow microspheres with three concentric multi-shells showed the best cycling performance, demonstrating excellent stability and a reversible capacity of up to 1702 mA h g−1 at a current density of 50 mA g−1. The electrode performance is attributed to the large specific surface area and enhanced volumetric capacity of the multi-shelled hollow spheres that provide maximum lithium storage, while the porous thin shells facilitate rapid electrochemical kinetics and buffer mechanical stresses that accompany volume changes during de/lithiation.

Multishelled TiO2 hollow microspheres as anodes with superior reversible capacity for lithium ion batteries

Herein, uniform multishelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, intershell spacing, and number of internal multishells, which are achieved by controlling the size, charge, and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multishelled TiO2 hollow microspheres show excellent rate capacity, good cycling performance, and high specific capacity. A superior capacity, up to 237 mAh/g with minimal irreversible capacity after 100 cycles is achieved at a current rate of 1 C (167.5 mA/g), and a capacity of 119 mAh/g is achieved at a current rate of 10 C even after 1200 cycles.

Quintuple-Shelled SnO2 Hollow Microspheres with Superior Light Scattering for High-Performance Dye-Sensitized Solar Cells

Quintuple-shelled SnO2 hollow microspheres are prepared by a hard-template method. DSSCs constructed with SnO2 multi-shell photoanodes show a record photoconversion efficiency of 7.18% due to enhanced light scattering. SnO2 hollow microspheres that are utilized as a scattering layer on top of P25 films increase the DSSC photoconversion efficiency from 7.29% to 9.53%.

A novel and highly efficient photocatalyst based on P25-graphdiyne nanocomposite.

Titania nanoparticles (P25) are successfully chemically bonded with graphdiyne (GD) nanosheets by a facile hydrothermal treatment, to form a novel nanocomposite photocatalyst. The as-prepared P25-GD nanocomposite exhibits higher photocatalytic activity for degrading methylene blue under UV irradiation than not only P25 and P25-carbon nanotube composite but also the current well-known P25-graphene composite photocatalysts. Moreover, P25-GD also shows considerable visible-light-driven photocatalytic activity, since the formation of chemical bonds between P25 and GD effectively decreases the bandgap of P25 and extends its absorbable light range. The photocatalytic activity of P25-GD can be adjusted by changing the content of GD in composites and the optimized value is about 0.6 wt%. Such a nanocomposite photocatalyst might find potential application in a wide range of fields including air purification and waste water treatment.

Hierarchical nanoscale multi-shell Au/CeO2 hollow spheres

Multi-shell ceria hollow spheres (MSCHSs) with a uniform size of ∼300 nm and controlled shell number up to quadruple were synthesized using carbonaceous spheres as the template in a process combining hydrothermally enhanced metal cation adsorption and tunable calcination. The featured sizes of these MSCHSs are in the hierarchical nanoscale region, including the diameters of the interior and exterior hollow spheres (80–300 nm), the thickness of the shells (∼30 nm), the distance between shells (<100 nm), and the pore size in the shells (∼4 nm), which meant that the as-synthesized MSCHSs possess not only a large specific surface area (∼90 m2 g−1) and narrow mesopore distribution, but also nanosized interconnected chambers. With these structural characteristics, the MSCHSs show fascinating capacities as good hosts for noble metals. Gold nanoparticles with sizes below 5 nm could be loaded on these MSCHSs with a high content and good dispersity to construct effective catalysts, which demonstrated a much improved catalytic performance in the reduction of p-nitrophenol. The optimal values of the reaction rate constant (k) reached up to 0.96 min−1. Moreover, this approach opens up a new way to form nanosized multi-shell structures, especially for those with large cation radii.

The role of spontaneous polarization in the negative thermal expansion of tetragonal PbTiO3-based compounds

PbTiO(3)-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO(3)-0.3BiFeO(3) and 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3), whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (δz(Pb/Bi)) is weakened in 0.7PbTiO(3)-0.3BiFeO(3) but well-maintained in 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3). There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi-O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides.

pH-Regulated Synthesis of Multi-Shelled Manganese Oxide Hollow Microspheres as Supercapacitor Electrodes Using Carbonaceous Microspheres as Templates

Multi‐shelled Mn2O3 hollow microspheres have been achieved through a pH‐regulated method and used as supercapacitor electrodes. The designed unique architecture allows efficient use of pseudo‐capacitive Mn2O3 nanomaterials for charge storage with facilitated transport for both ions and electrons, rendering them high specific capacitance, good rate capability, and remarkable cycling performance.

Zero Thermal Expansion and Ferromagnetism in Cubic Sc1–xMxF3 (M = Ga, Fe) over a Wide Temperature Range

The rare physical property of zero thermal expansion (ZTE) is intriguing because neither expansion nor contraction occurs with temperature fluctuations. Most ZTE, however, occurs below room temperature. It is a great challenge to achieve isotropic ZTE at high temperatures. Here we report the unconventional isotropic ZTE in the cubic (Sc1-xMx)F3 (M = Ga, Fe) over a wide temperature range (linear coefficient of thermal expansion (CTE), αl = 2.34 × 10(-7) K(-1), 300-900 K). Such a broad temperature range with a considerably negligible CTE has rarely been documented. The present ZTE property has been designed using the introduction of local distortions in the macroscopic cubic lattice by heterogeneous cation substitution for the Sc site. Even though the macroscopic crystallographic structure of (Sc0.85Ga0.05Fe0.1)F3 adheres to the cubic system (Pm3̅m) according to the results of X-ray diffraction, the local structure exhibits a slight rhombohedral distortion. This is confirmed by pair distribution function analysis of synchrotron radiation X-ray total scattering. This local distortion may weaken the contribution from the transverse thermal vibration of fluorine atoms to negative thermal expansion, and thus may presumably be responsible for the ZTE. In addition, the present ZTE compounds of (Sc1-xMx)F3 can be functionalized to exhibit high-Tc ferromagnetism and a narrow-gap semiconductor feature. The present study shows the possibility of obtaining ZTE materials with multifunctionality in future work.

Precursor-induced fabrication of β-Bi2O3 microspheres and their performance as visible-light-driven photocatalysts

Flower-like β-Bi2O3 microspheres with high specific surface area and excellent visible-light-driven photocatalytic activity (for degradation of Rhodamine B) were successfully synthesized via a facile hydrothermal process and subsequent calcination. By precisely adjusting the hydrothermal conditions, the composition and morphology of the microspherical precursors could be well controlled, so that upon further optimized calcination of the precursors, the selective formation of the monoclinic α-Bi2O3 and tetragonal β-Bi2O3 with three dimensional (3D) hierarchical architectures could be achieved. These tetragonal β-Bi2O3 microspheres with an average diameter of 3 μm were constructed by nanoflakes with an average thickness of 50 nm, which, as far as we know, is the first reported result on the 3D hierarchical architectures of tetragonal β-Bi2O3. Its flower-like microspherical architecture made the tetragonal β-Bi2O3 possess not only much improved specific surface area but also a narrower band gap, which significantly enhanced its visible-light-driven photocatalytic activity for the degradation of Rhodamine B (RhB). To further optimize the synthetic conditions and realize the controllable synthesis, the formation mechanism for the morphologies and polymorphs of the Bi2O3 microspheres was discussed in detail.

Multi-shelled LiMn2O4 hollow microspheres as superior cathode materials for lithium-ion batteries

Owing to its environmental-benignity, low-cost and abundance, spinel LiMn2O4 has long been considered as a promising cathode material for lithium-ion batteries (LIBs). However, the low electronic conductivity, small lithium diffusion coefficient and poor capacity retention hindered its further development and application. Herein, we report the synthesis of multi-shelled LiMn2O4 hollow microspheres through a hard template method, with the composition, shell number, shell thickness and porosity accurately controlled. Benefitting from the structural superiorities of multi-shelled hollow structures, the triple-shelled LiMn2O4 hollow microsphere exhibits a better cycling stability than all the reported results based on un-coated or un-doped LiMn2O4 (the capacity fading rate is 0.10% per cycle).