Synthetic method and application of the multi-shell hollow structure

Owing to the aesthetic beauty, unique structural features and fascinating physicochemical properties, multi-shell hollow structures (MSHSs) materials attached the tremendous interest of researchers. Comparing to the same-sized solid or single hollow counterparts, MSHSs materials show a mass of excellent properties. Despite the complex process resulting from the complicated structure, plenty of efforts have been made to the MSHSs materials during the past dacade due to its superior properties. The morphology and structure have a great influence on the property of materials. So the rational design of hollow structured materials is of great importance as both huge challenges in materials science and practical solutions for efficient energy utilization in modern society. In this review, we describe different synthetic methodologies for multi-shelled hollow structures and explain the correspond synthetic machanism in detail. The synthetic strategies for MSHSs can be divided into three types as follows, hard-templating methods, soft-templating methods and self-templating methods. Self-templating methods include Ostwald ripening, ion exchange, selective etching, thermally induced mass relocation and so on. Except for these, some particular strategies are used for synthesizing MSHSs with special morphology and structures owing to the complex interior structures. These materials show great prospects in dealing with the growing environmental concerns. So with the increasing demands for cleaner power sources, these materials have vast prospectives in the fields like lithium/sodium-ion batteries, supercapacitors, dye-sensitized solar cells, photocatalysis. As a unique family of functional materials, MSHSs own amounts of advantages, such as low density, large specific surface area, reduced charge-transport lengths and lots of active sites for reaction, which make them have a wide range of application. For example, the cavities of the MSHSs can effectively accommodate the volume effect during lithium/sodium de-intercalation for the lithium/sodium-ion battery (LIB/SIB) cathode materials like transition metal oxides, promote the sturctural stability and cycling performance. In supercapacitors, the large specific surface area of MSHSs can provide more active sites for redox reaction and increase the capacity. And the shorter charge transfer distance improves the rate performance of materials. In dye-sensitized solar cells (DSSCs) and photocatalysis, the presense of multi-shell promote the reflection and absorption of light, enhance the performance and improve the light throughput efficiency of DSSCs and the catalytic efficiency. Finally, although rapid development and great progress in synthetic methods of MSHSs have been made in recent years, the synthesis and application of MSHSs are still in the laboratory due to the limited research for the mechanism of synthetic methods. Therefore, there is still a long way to go for the commercial application of MSHSs materials. We believe that other advanced synthetic methodologies for MSHSs will be developed in the future and all the obstructions hinder the wide range application of MSHSs will be solved.