Ball-in-cage nanocomposites of metal-organic frameworks and three-dimensional carbon networks: synthesis and capacitive performance.

In order to improve the electrical conductivity of metal-organic frameworks (MOFs) which have drawn remarkable attention owing to their potential application in the energy storage field, a Co-based zeolitic imidazolate framework (ZIF-67) polyhedron was in situ integrated into a three-dimensional carbon network (3DCN) to construct a Ball-in-Cage (BIC) nanostructure. The introduced 3DCN acting as the electronic pathway can provide nucleation sites for MOF particles; consequently, further growth of the MOF particles is limited by the size effect of 3DCN. The BIC frame not only controls the MOF particle size, but also ensures a high electron conductivity of the entire structure. The as-prepared BIC electrode displays an outstanding capacitance of 119 F g-1 at a current density of 0.5 A g-1 and a great rate performance as well, which can be expected to be a promising approach to enhance the electrochemical performance of pristine MOFs in the future.