Nitrogen-doped microporous carbon spheres (NMCSs) are successfully prepared via carbonization and KOH activation of phenol-formaldehyde resin polymer spheres synthesized by a facile and time-saving one-step hydrothermal strategy using triblock copolymer Pluronic F108 as a soft template under the Stöber-like method condition. The influence of the ethanol/water volume ratios and carbonation temperatures on the morphologies, pore structures and electrochemical performances of the prepared NMCSs are investigated systematically. The optimal NMCSs have a large specific surface area of 1517 m2 g− 1 with a pore volume of 0.8 cm3 g− 1. The X-ray photo-electron spectroscopy analysis reveals a suitable nitrogen-doped content of 2.6 at.%. The as-prepared NMCSs used as supercapacitor electrode materials exhibit an outstanding specific capacitance of 416 F g− 1 at a current density of 0.2 A g− 1, also it shows an excellent charge/discharge cycling stability with 96.9% capacitance retention after 10,000 cycles. The constructed symmetric supercapacitors using PVA/KOH as the gel electrolyte can deliver a specific capacitance of 60.6 F g− 1 at current density of 1 A g− 1. A maximum energy density of 21.5 Wh kg− 1 can be achieved at a power density of 800 W kg− 1, and the energy density still maintains 13.3 Wh kg− 1 even at a high power density of 16 kW kg− 1. The results suggest that this work can open up a facile and effective way to synthesize the NMCSs for electrode materials of high performance energy storage devices.Electronic supplementary materialThe online version of this article (10.1186/s11671-018-2713-0) contains supplementary material, which is available to authorized users.

Carbon nanospheres with distinguishable microstructure were prepared by carbonization and subsequent KOH activation of F108/resorcinol-formaldehyde composites. The dosage of triblock copolymer Pluronic F108 is crucial to the microstructure differences. With the adding of F108, the polydisperse carbon nanospheres (PCNS) with microporous structure, monodisperse carbon nanospheres (MCNS) with hierarchical porous structure, and agglomerated carbon nanospheres (ACNS) were obtained. Their microstructure and capacitance properties were carefully compared. As a result of the synergetic effect of mono-dispersion spheres and hierarchical porous structures, the MCNS sample shows improved electrochemical performance, i.e., the highest specific capacitance of 224 F g−1 (0.2 A g−1), the best rate capability (73% retention at 20 A g−1), and the most excellent capacitance retention of 93% over 10,000 cycles, making it to be the promising electrode material for high-performance supercapacitors.

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Hierarchical porous carbon spheres (HPCSs) have been widely used in energy storage and conversion due to their open framework, high specific surface area and chemical stability. Here, we report a novel and facile method to synthesize porous phenolic resin spheres through an in situ pore self-formed strategy. The phenolic resin spheres can directly transform into sulfur-doped HPCSs by carbonization and activation. The hierarchical porous structure maximizes the specific surface area and facilitates ion diffusion and transport. Combine with the hierarchical porous structure, high specific surface area and suitable S doping content, the HPCSs-based symmetric supercapacitor presents high energy density of 12 Wh kg−1 and outstanding power output capability of 28 kW kg−1. This methodology provides a new way for the preparation of HPCSs and other functional porous carbon spheres with adjustable pore structure and surface properties.

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