Three-Dimensional Nickel Oxide@Carbon Hollow Hybrid Networks with Enhanced Performance for Electrochemical Energy Storage

• Novel NiO@C hollow hybrid networks (HHNs) consisted of nanotubes with interconnected branches were designed and fabricated via ZnO template-assisted electrodeposition method.
• The NiO@C HHNs represent a new example of hollow nanomaterials and show the following advantages as electrodes: i) The carbon layers will provide electron “highways” for charge storage and delivery; ii) The hollow structures in HHNs will obviously enhance the utilization rates of carbon and NiO materials, relax transport of ions, enable fast/reversible faradic reactions and provide short ion diffusion paths; iii) The network structures can avoid NiO aggregation or stacking during electrochemical charge-discharge cycling and can effectively maintain the active surface and leave stable and open channels for ion transport; iv) The network structures can act as an ideal strain buffer to accommodate volume changes in a fixed direction, and accordingly they have a much better resilience and structural stability in the electrochemical charge/discharge process.
• The NiO@C HHNs electrodes show excellent cycle performance (almost no capacitance loss after 2000 cycles) and exhibit superior rate capability (∼14% Csp decay with scan rate increasing from 5 to 100 mV/s).

In this paper, the novel nickel oxide@carbon (NiO@C) hollow hybrid networks (HHNs) consisted of nanotubes with interconnected branches are designed and fabricated via template-assisted electrodeposition method. Electrochemical measurements demonstrate that the NiO@C HHNs electrodes exhibit high specific capacitance (Csp) (572.5 F/g) at current density of 2.5 A/g, which is more than twice as that of NiO hollow networks (HNs) electrode (259.6 F/g). The NiO@C HHNs electrodes show high flexibility and excellent cycle performance (almost no capacitance loss after 2000 cycles) and exhibit superior rate capability (∼14% Csp decay with scan rate increasing from 5 to 100 mV/s). The assembled asymmetric supercapacitors (ASCs) based on NiO@C HHNs as positive electrodes and 3D active carbon (AC) as negative electrodes also shows high specific capacitance, excellent cycle performance, and high energy and power densities. Two ASC device units connected in series could drive a red light-emitting diode (LED, 2.0 V) well for more than 60 s after charging at 28 A/g for 10 s. The above results indicate that the NiO@C HHNs own promising potential for electrochemical energy storage.

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