Hierarchical walnut-like Ni0.5Co0.5O hollow nanospheres (NCO-HNS) were successfully synthesized via a facile and effectual hard-template method. Layered Ni0.5Co0.5O nanosheets stacked by several ultra-thin layers with the thickness of 2–3 nanometers were self-assembled into the hollow nanospheres. This unique hierarchical architecture, including micro-, meso-, and macropores, could provide a large specific surface area (123.7 m2 g−1) and efficient channel for the diffusion of ions and electrons, as well as the penetration of electrolyte. Significantly, the as-prepared NCO-HNS exhibit an excellent specific capacity of 221.9 mA h g−1 at the current density of 1 A g−1, a remarkable rate capability (172.8 mA h g−1 at 20 A g−1) and capacity retention (99.4% after 3000 cycles). Moreover, the NCO-HNS was then successfully fabricated into hybrid devices with active carbon. These devices deliver a maximum energy density of 38.3 W h kg−1 (31.8 W h L−1) at the power density of 743.5 W kg−1. Note that because of the morphology and hierarchical architecture, the energy density of the device could still maintain 19.3 W h kg−1 (16.0 W h L−1) even at an ultra-high power density of 7604.9 W kg−1. These hierarchical walnut-like Ni0.5Co0.5O hollow nanospheres comprising layered nanosheets may have potential as battery-type electrode materials for advanced energy storage devices.

•Ni0.54Co0.46O2 grown on carbon fibers as binder-free electrode for supercapacitor directly.•The coexistence of Ni2+ and Ni3+ in Ni0.54Co0.46O2 could boost the performance.•The products exhibit outstanding specific capacity and rate performance.•Symmetrical device delivers excellent energy density and power density.Hierarchical Ni0.54Co0.46O2 architectures composed by nanowires or nanosheets were successfully grown on bio-mass carbon fiber cloth (CFC) by hydrothermal method. The morphology of Ni0.54Co0.46O2 can be effectively controlled by using different precipitators. The structural effects of the two kinds of morphologies were researched. the results suggest that the Ni0.54Co0.46O2 nanosheet arrays grown on CFC (NCO-NSs/CFC) shows a higher Faradaic areal capacity of 438 μAh cm−2 (238.1 mAh g−1) at a current density of 1 mA cm−2 and still about 90.3% initial capacity retention even at the high current density of 50 mA cm−2. Moreover, an all-solid-state flexible symmetric supercapacitor device has been successfully assembled. The optimized device delivers superior electrochemical performance with an outstanding energy density of 92.4 Wh kg−1 at a power density of 207.2 W kg−1. Such hierarchical nanostructure composed by well-aligned uniform Ni0.54Co0.46O2 nanosheet arrays grown on bio-mass carbon fiber cloth might hold great promise as battery-type electrode material for high-performance supercapacitor.

•HPCNFs are fabricated by electrospinning.•DMF/THF mixed solvent can disperse CaCO3 uniformly in precursor solution.•The HPCNF mats are binder-free using to electrode.•Excellent electrochemical performances are achieved.1D hierarchical porous carbon nanofibers (HPCNFs) are prepared via electrospinning ternary PAN/N, N’-dimethylformamide (DMF)/tetrahydrofurar (THF) and using commercially available nano-CaCO3 as template. In the process of carbonization, nano-CaCO3 template decomposes and releases CO2 to form micropores and mesopores. Macropores are generated by removing the CaO nanoparticles using acid subsequently. The hierarchical pores are fairly well distributed because the nano-CaCO3 particles are highly dispersed in the fiber due to the better wettability in binary solvent. The obtained HPCNFs attain high specific surface area without physical and chemical activation. The HPCNF mats, possessing free-standing architecture, are used as binder-free electrodes for supercapacitor. Because of high specific surface area, rational pore diameter distribution and binder-free characterization of electrodes, the HPCNFs display a high capacitance of 251 F g−1 at a current density of 0.5 A g−1 as well as excellent rate capability and outstanding cycling stability (over 88% capacitance retention after 5000 cycles at the current density of 1 A g−1). These results demonstrate that the binary solvent method is effective to achieve high-performance electrode materials and it has a promising prospect on applications of energy storages.

Multichannel carbon nanofibers (MCNFs) have been fabricated by annealing electrospun PAN/PS immiscible polymer nanofibers. The obtained mechanically flexible mats of MCNFs, possessing an integrative architecture, are used as an electrode directly with no binder and without any activation processes. Owing to the binder-free characteristic, unique multichannel structure and high specific surface area, the MCNFs show high capacitance (270 F g−1 at a current density of 0.5 A g−1), perfect cycling stability (the capacitance does not decrease after 5000 cycles at a current density of 1 A g−1), excellent rate capability (89% retention at a current density of 20 A g−1) and high energy and power density. These results demonstrate that the electrode material has a promising prospect in applications of energy storage.

Hierarchical walnut-like Ni0.5Co0.5O hollow nanospheres (NCO-HNS) were successfully synthesized via a facile and effectual hard-template method. Layered Ni0.5Co0.5O nanosheets stacked by several ultra-thin layers with the thickness of 2–3 nanometers were self-assembled into the hollow nanospheres. This unique hierarchical architecture, including micro-, meso-, and macropores, could provide a large specific surface area (123.7 m2 g−1) and efficient channel for the diffusion of ions and electrons, as well as the penetration of electrolyte. Significantly, the as-prepared NCO-HNS exhibit an excellent specific capacity of 221.9 mA h g−1 at the current density of 1 A g−1, a remarkable rate capability (172.8 mA h g−1 at 20 A g−1) and capacity retention (99.4% after 3000 cycles). Moreover, the NCO-HNS was then successfully fabricated into hybrid devices with active carbon. These devices deliver a maximum energy density of 38.3 W h kg−1 (31.8 W h L−1) at the power density of 743.5 W kg−1. Note that because of the morphology and hierarchical architecture, the energy density of the device could still maintain 19.3 W h kg−1 (16.0 W h L−1) even at an ultra-high power density of 7604.9 W kg−1. These hierarchical walnut-like Ni0.5Co0.5O hollow nanospheres comprising layered nanosheets may have potential as battery-type electrode materials for advanced energy storage devices.