Rongfang Zhao

Petal-like MoS2 Nanosheets Space-Confined in Hollow Mesoporous Carbon Spheres for Enhanced Lithium Storage Performance

An innovative approach for efficient synthesis of petal-like molybdenum disulfide nanosheets inside hollow mesoporous carbon spheres (HMCSs), the yolk-shell structured MoS2@C, has been developed. HMCSs effectively control and confine in situ growth of MoS2 nanosheets and significantly improve the conductivity and structural stability of the hybrid material. The yolk-shell structured MoS2@C is proven to achieve high reversible capacity (993 mA h g-1 at 1 A g-1 after 200 cycles), superior rate capability (595 mA h g-1 at a current density of 10 A g-1), and excellent cycle performance (962 mA h g-1 at 1 A g-1 after 1000 cycles and 624 mA h g-1 at 5 A g-1 after 400 cycles) when evaluated as an anode material for lithium-ion batteries. This superior performance is attributed to the yolk-shell structure with conductive mesoporous carbon as the shell and the stack of two-dimensional MoS2 nanosheets as the yolk.

Synthesis of 1D upconversion CeO2:Er, Yb nanofibers via electrospinning and their performance in dye-sensitized solar cells

1D upconversion CeO2:Er, Yb nanofibers, which could absorb NIR light and upconvert it to visible light, to increase the photocurrent of DSSCs has been fabricated by an electrospinning method. The products were confirmed by transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and X-ray diffraction (XRD), and fluorescence spectroscopy (PL) techniques. An enhancement of 14% in the light harvesting efficiency was observed due to the upconversion and scattering effect. It is anticipated that these nanostructures may provide a new direction for CeO2 application in DSSCs.

Heterogeneous Double-Shelled Constructed Fe3O4 Yolk–Shell Magnetite Nanoboxes with Superior Lithium Storage Performances

Among the numerous candidate materials for lithium ion batteries, ferroferric oxide (Fe3O4) has been extensively concerned as a prospective anode material because of its high theoretical specific capacity, abundant resources, low cost, and nontoxicity. Here, we designed and fabricated a unique yolk-shell construction by generating heterogeneous double-shelled SnO2 and nitrogen-doped carbon on Fe3O4 yolk (denoted as Fe3O4@SnO2@C-N nanoboxes). The yolk-shell structured Fe3O4@SnO2@C-N nanoboxes have the adjustable void space, which permits the free expansion of Fe3O4 yolks without breaking the double shells during the lithiation/delithiation processes, avoiding the structural pulverization. Moreover, the heterogeneous double-shelled SnO2@C-N can meaningfully improve the electronic conductivity and enhance the lithium storage performance. Two metal oxides also show the specific synergistic effect, promoting the electrochemistry reaction. As a result, this yolk-shell structured Fe3O4@SnO2@C-N exhibits high specific capacity (870 mA h g-1 at 0.5 A g-1 after 200 cycles), superior rate capability, and long cycle life (670 mA h g-1 at 3 A g-1 after 600 cycles). This design and construction method can be extended to synthesize other yolk-shell nanostructured anode materials with improved electrochemistry performance.

Theoretical investigation of pillar[4]quinone as a cathode active material for lithium-ion batteries

AbstractThe applicability of a novel macrocyclic multi-carbonyl compound, pillar[4]quinone (P4Q), as the cathode active material for lithium-ion batteries (LIBs) was assessed theoretically. The molecular geometry, electronic structure, Li-binding thermodynamic properties, and the redox potential of P4Q were obtained using density functional theory (DFT) at the M06-2X/6-31G(d,p) level of theory. The results of the calculations indicated that P4Q interacts with Li atoms via three binding modes: Li–O ionic bonding, O–Li···O bridge bonding, and Li···phenyl noncovalent interactions. Calculations also indicated that, during the LIB discharging process, P4Q could yield a specific capacity of 446 mAh g−1 through the utilization of its many carbonyl groups. Compared with pillar[5]quinone and pillar[6]quinone, the redox potential of P4Q is enhanced by its high structural stability as well as the effect of the solvent. These results should provide the theoretical foundations for the design, synthesis, and application of novel macrocyclic carbonyl compounds as electrode materials in LIBs in the future. Graphical AbstractSchematic representation of the proposed charge-discharge mechanism of Pillar[4]quinone as cathode for lithium-ion batteries

Ultrathin WS2 nanosheets vertically embedded in a hollow mesoporous carbon framework – a triple-shell structure with enhanced lithium storage and electrocatalytic properties

Ultrathin WS2 nanosheets are vertically embedded in hollow mesoporous carbon spheres (HMCSs) to form unique hierarchical triple-shell (WS2–C–WS2) hollow nanospheres, i.e. HTSHNs WS2/C, via a facile and scalable hydrothermal method. The as-synthesized HTSHNs WS2/C nanocomposites are confirmed to have an expanded interlayer spacing of WS2 with chemical bonding between WS2 and HMCSs. The expanded WS2 interlayer spacing contributes to the enhancement of the kinetics of ion/electron transport and the improvement of the electrochemical performance of the HTSHNs WS2/C. As a result, the optimized HTSHNs WS2/C composites deliver a superior rate capability of 396 mA h g−1 at 10 A g−1, and stable cycling performance up to 1000 cycles, presenting a capacity of 784 and 442 mA h g−1 at 1 and 5 A g−1, respectively. Additionally, HTSHNs WS2/C provide abundant catalytically active sites for the enhancement of the electrocatalytic activity for the hydrogen evolution reaction (HER).

Nitrogen-doped mesoporous hollow carbon nanoflowers as high performance anode materials of lithium ion batteries

Nitrogen-doped mesoporous hollow carbon nanoflowers (N-HCNF) are successfully prepared by a facile hard-template route via a hydrothermal process, subsequent carbonization and etching. The as-synthesized N-HCNF has high specific surface area (507.5 m2 g−1) and unique nanostructure, which make N-HCNF a potential anode material for lithium ion batteries. In the electrochemical test, the as-prepared N-HCNF exhibit high specific capacity, markedly improve cycle stability, and enhance rate performance compared with nitrogen-doped hollow carbon nanorods (N-HCNR) and hollow carbon nanoflowers (HCNF). The as-prepared N-HCNF displays a reversible specific capacity of 528 mA h g−1 after 1000 cycles at 2C. N-HCNF shows the excellent rate performance and the stable capacity of N-HCNF maintains 298 mA h g−1 at 10C. The significant electrochemical property improvements of N-HCNF are attributed to the large BET surface area, N-doped carbon shell and unique 3D hollow nanostructure of N-HCNF.