Hollow nano- and microstructures: Mechanism, composition, applications, and factors affecting morphology and performance

Hollow nano- and microstructures with controlled shape, size, pore volume, shell thickness, and composition have been considered as an emerging class of materials for versatile applications. These structures provide interior voids with porous shells, which endow them with heterogeneous interfaces and high specific area beneficial for various applications. Herein, we summarized the plausible formation mechanisms (i.e., template-mediated approach, Kirkendall effect, Ostwald ripening, thermal decomposition, galvanic replacement, and ion-exchange) and possible compositions (i.e., organic, inorganic, and hybrid) in the fabrication of hollow nano- and microstructures. Furthermore, hollow nano- and microstructure-based oxides, hydroxides, sulfides, selenides, phosphides, carbon, and their hybrids as advanced electrode materials for supercapacitors (SCs) and some other applications have been recapitulated. Moreover, the factors affecting their morphological shapes (i.e., time, concentration, and temperature) and performances (i.e., number of shells, size and thickness of shells, and morphology) have also been discussed. Finally, the current review article ends with future research direction and prospective allowing the further growth of these structures in the research field and future applications. We believe this review article will open a new avenue and shed some lights on the development of future advanced electrode materials for next-generation energy storage devices as well as other applications.