Preparation of Hollow Nitrogen Doped Carbon via Stresses Induced Orientation Contraction.

Hollow structured materials are widely applicable in various fields. Although many routes have been explored for getting such materials, a strategy mainly based on physical effect is still deficient. Herein, a "stresses induced orientation contraction" mechanism for preparation of hollow structures is reported. The composites constructed by zeolite imidazolate framework-8 (ZIF8) cores and polymerized dopamine (PDA) shells, upon annealing, form intensive interfacial interactions, which drag the ZIF8 cores outward to restrain their shrinkage. The gradually accumulated stresses in the central position of ZIF8 dodecahedron nanoparticles, then destroy the ZIF8 crystalline cores to form the hollow structures. In this stress-based route for creating hollow interiors with core-shell composites as the starting materials, three critical factors are necessary: 1) an intensive core-shell interfacial interaction; 2) the distinctly higher shrinkage degree of the cores than the shells; and 3) the relatively loose core structures. In oxygen reduction reaction (ORR) tested with three-electrode solution system and Zn-O2 battery, the achieved hollow nitrogen doped carbon (NC) demonstrates ultrahigh catalytic activities. This work gives an absolutely novel strategy for preparation of hollow structures, which may afford the exploration of a wider range of materials system with hollow interiors.