Nitrogen-Doped Hollow Carbon Nanospheres for High-Performance Li-Ion Batteries

N-doped carbon materials is of particular attraction for anodes of lithium-ion batteries (LIBs) because of their high surface areas, superior electrical conductivity, and excellent mechanical strength, which can store energy by adsorption/desorption of Li⁺ at the interfaces between the electrolyte and electrode. By directly carbonization of zeolitic imidazolate framework-8 nanospheres synthesized by an emulsion-based interfacial reaction, we obtained N-doped hollow carbon nanospheres with tunable shell thickness (20 nm to solid sphere) and different N dopant concentrations (3.9 to 21.7 at %). The optimized anode material possessed a shell thickness of 20 nm and contained 16.6 at % N dopants that were predominately pyridinic and pyrrolic. The anode delivered a specific capacity of 2053 mA h g^–1 at 100 mA g^–1 and 879 mA h g^–1 at 5 A g^–1 for 1000 cycles, implying a superior cycling stability. The improved electrochemical performance can be ascribed to (1) the Li⁺ adsorption dominated energy storage mechanism prevents the volume change of the electrode materials, (2) the hollow nanostructure assembled by the nanometer-sized primary particles prevents the agglomeration of the nanoparticles and favors for Li⁺ diffusion, (3) the optimized N dopant concentration and configuration facilitate the adsorption of Li⁺; and (4) the graphitic carbon nanostructure ensures a good electrical conductivity

Hollow Metal–Organic Framework Nanospheres via Emulsion-Based Interfacial Synthesis and Their Application in Size-Selective Catalysis

Metal–organic frameworks (MOFs) represent an emerging class of crystalline materials with well-defined pore structures and hold great potentials in a wide range of important applications. The functionality of MOFs can be further extended by integration with other functional materials, e.g., encapsulating metal nanoparticles, to form hybrid materials with novel properties. In spite of various synthetic approaches that have been developed recently, a facile method to prepare hierarchical hollow MOF nanostructures still remains a challenge. Here we describe a facile emulsion-based interfacial reaction method for the large-scale synthesis of hollow zeolitic imidazolate framework 8 (ZIF-8) nanospheres with controllable shell thickness. We further demonstrate that functional metal nanoparticles such as Pd nanocubes can be encapsulated during the emulsification process and used for heterogeneous catalysis. The inherently porous structure of ZIF-8 shells enables encapsulated catalysts to show size-selective hydrogenation reactions