Hollow Multishelled Structures for Promising Applications: Understanding the Structure-Performance Correlation.

Abstract

The unique structural features of hollow multishelled structures (HoMSs) endow them with abundant beneficial physicochemical properties including high surface-to-volume ratio, low density, short mass transport length, and high loading capacity. As a result, HoMSs have been considered as promising candidates for various application areas including energy storage, electromagnetic wave (EW) absorption, catalysis, sensors, drug delivery, etc. However, for a long time, the general and controllable synthesis of HoMSs has remained a great challenge using conventional soft-templating or hierarchical self-assembly methods, which severely limits the development of HoMSs. Fortunately, the sequential templating approach (STA), which was first reported by our group and further developed by others, has been proven to be a versatile method for HoMS fabrication. By using the STA and through accurate physical and chemical manipulation of the synthesis conditions, the diversity of the HoMS family has been enriched in both compositional and geometrical aspects. Benefiting from the flourishing of synthetic methodology, various HoMSs have been fabricated and showed application prospect in diverse areas. However, the structure-performance correlation remained obscure, which hinders the design of optimal HoMSs to achieve the best application performance. This Account aims to explore the correlation between HoMS structural characteristics and their application performance. We first briefly summarize the achievements in the compositional and geometrical manipulation of HoMSs by physically and chemically tuning the synthesis process. Then, we systematically discuss the effect of structural engineering on optimizing performance in various application areas, especially for energy storage, EW absorption, catalysis, sensors, and drug delivery. Specifically, HoMSs with multiple thin shells can provide numerous active sites for energy storage, leading to a higher volumetric energy density than their single-shelled counterparts. The high shell porosity permits electrolyte access to the interior of HoMSs, along with shortened mass transport path through the thin shells, resulting in a high power density. The adequate inner cavity effectively buffers the ion-insertion strain, leading to prolonged cycling stability. For EW absorption, HoMSs with high surface-to-volume ratio can provide many sites for EW-sensitive material loading. The multiple separated shells with small intershell space enable multiple EW reflection and scattering, thus improving EW absorption efficiency. For catalysis and sensors, the increased reaction sites along with the facilitated transport of reactants and products can enhance the activity and sensitivity. The selectivity can be improved by optimizing the pore structure and hydrophobic or hydrophilic properties of the shells. Also the stability is improved with inner shells being protected by exterior ones. For drug delivery, the increased exposed sites and the inner cavity improve the drug loading capacity. The adjustable pore structure along with accurately designed shell composition leads to well-targeted drug release responding to different stimuli at different targeting sites. The multiple separated shells endow HoMSs with sustained drug release step-by-step from inside to outside. These in-depth understandings on the structure-performance correlation can guide the design of ideal HoMSs to satisfy the specific requirements for different application areas, thus further improving the application performance and expanding the HoMSs family.