Zhenghong Dong

Accurate Control of Multishelled Co3O4 Hollow Microspheres as High-Performance Anode Materials in Lithium-Ion Batteries

More than just an empty shell: Multishelled Co3O4 microspheres were synthesized as anode materials for lithium-ion batteries in high yield and purity. As their porous hollow multishell structure guarantees a shorter Li+ diffusion length and sufficient void space to buffer the volume expansion, their rate capacity, cycling performance, and specific capacity were excellent (1615.8 mA?h?g-1 in the 30th cycle for triple-shelled Co3O4; see graph).

General Synthesis and Gas-Sensing Properties of Multiple-Shell Metal Oxide Hollow Microspheres

Hollow spheres with nanometer-to-micrometer dimensions, controlled internal structure, and shell composition have attracted tremendous attention because of their potential application in catalysis, drug delivery, nanoreactors, energy conversion and storage systems, photonic devices, chemical sensors, and biotechnology. Single-shell and double-shell hollow spheres of various compositions have been synthesized by a number of methods, such as vesicles, emulsions, micelles, gas-bubble, and hard-templating methods. More recently, efforts have focused on the fabrication of hollow spheres with multiple shells, as these materials are expected to have better properties for applications such as drug release with prolonged release time, heterogeneous catalysis, lithiumion batteries, and photocatalysis. For example, multipleshell hollow microspheres of Cu2O have been prepared by vesicle templating and an intermediate-templating phasetransformation process. Multiple-shell azithromycin hollow microspheres were fabricated by hierarchical assembly. Cao and co-workers reported the synthesis of tripleshelled SnO2 hollow microspheres by chemically induced selfassembly in the hydrothermal environment which exhibited enhanced electrochemical performance. Yao and co-workers reported excellent cycle performance and enhanced lithium storage capacity of multiple-shell Co3O4 hollow microspheres synthesized by oriented self-assembly. These preparative methods, however, are suited for each specific material and cannot be applied generally to a wide range of materials. Currently, there is no general synthetic approach for fabricating multiple-shell hollow nanostructures of any desired material. Herein, we present a straightforward and general strategy to prepare metal oxide hollow microspheres with a controlled number of shells. Carbonaceous microspheres were used as sacrificial templates. The microspheres were saturated with a desired metal salt solution and then heated in air; the carbonaceous template evaporates and templates the formation of metal oxide shells. The number of shells is controlled by the metal ion loading and the process is general for a wide range of metal oxide materials. Scheme 1 illustrates the general process of fabricating multiple-shell hollow metal oxide microspheres. The key to this process is the use of carbonaceous particles rich with surface functional groups available for metal ion adsorption.

Accurate Control of Multishelled ZnO Hollow Microspheres for Dye-Sensitized Solar Cells with High Efficiency

A series of multishelled ZnO hollow microspheres with controlled shell number and inter-shell spacing have been successfully prepared by a simple carbonaceous microsphere templating method, whose large surface area and complex multishelled hollow structure enable them load sufficient dyes and multi-reflect the light for enhancing light harvesting and realize a high conversion efficiency of up to 5.6% when used in dye-sensitized solar cells.

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%.

Resonance-Enhanced Absorption in Hollow Nanoshell Spheres with Omnidirectional Detection and High Responsivity and Speed

Optical resonance formed inside a nanocavity resonator can trap light within the active region and hence enhance light absorption, effectively boosting device or material performance in applications of solar cells, photodetectors (PDs), and photocatalysts. Complementing conventional circular and spherical structures, a new type of multishelled spherical resonant strategy is presented. Due to the resonance-enhanced absorption by multiple convex shells, ZnO nanoshell PDs show improved optoelectronic performance and omnidirectional detection of light at different incidence angles and polarization. In addition, the response and recovery speeds of these devices are improved (0.8 and 0.7 ms, respectively) up to three orders of magnitude faster than in previous reports because of the existence of junction barriers between the nanoshells. The general design principles behind these hollow ZnO nanoshells pave a new way to improve the performance of sophisticated nanophotonic devices.