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Herein, we report the preparation of an effective and novel NiCo2O4 dendritic structure with nanothorn arrays, using a stepwise, bottom-up hydrothermal and self-sacrificial template method. Rod-like ZnO is synthesized on Ni foam as self-sacrificing template, and Ni-Co-based precursor is grown on it through a hydrothermal method. NiCo2O4 dendritic crystals are obtained by alkali etching of the template and calcination, which significantly enhance its performance on electrochemical energy storage. Although the ZnO matrix is removed by alkali etching, it provides a basis for the growth of Ni-Co oxide. Using ZnO as template is simple to operate and can directly determine the shape and size of the hollow structure. Meanwhile, the ZnO template core can be well separated from the hollow structure, and the template can be used without surface functionalization, which is more simple and efficient. The obtained material can be directly used as electrode material without further processing, offering the benefit of unique structural advantages and low electron transmission resistance, as there is no need to use a binder. The as-obtained NiCo2O4 nanothorn electrode exhibits excellent electrochemical performance. It shows ultrahigh specific capacitance of 1534 C g-1 at 1 A g-1 current density, good rate discharge performance (75.8% retention from 0.5 A g-1 to 5 A g-1), values superior to those of nanothorn NiO, Co3O4 and bare Ni-Co 1-2 nanosheet structures and excellent cycling ability (83% retention after 5000 cycles). The as-assembled Ni-Co 1-2//AC hybrid supercapacitor device also exhibits high energy density of 64.1 Wh kg-1 at the power density of 450 W kg-1.

Herein, a novel preparation route of bimetallic spherical core-shell particles of immiscible metal system was developed and demonstrated through the synthesis of Fe@Cu core–shell microsphere particles. Copper ferrite (CuFe2O4) was used as precursor for the preparation of the Core–shell structured Fe@Cu microsphere using the solid-state immiscibility of Fe and Cu and the low wettability strategy of the liquid-solid interface of graphite at 1403 K. The results showed that phase separation occurred between Cu and Fe, where Cu tended to move towards the surface of the particles and Fe was more concentrated in the center of the particles, due to the lower surface energy of liquid Cu with respect to solid Fe. This was followed by formation of metal droplets located on loose graphite flakes on the spherical Fe@Cu due to the solid-liquid interfacial tension. The as-prepared Fe@Cu microsphere exhibited good spherical shapes and smooth surfaces. The cross-sectional micrographics and element mapping of the spherical particles confirmed the evenly distributions of the Fe-rich core and Cu-rich shell. This strategy is promising for the fabrication of core–shell structured spherical particles for immiscible alloys.