Heteroatoms in situ-doped hierarchical porous hollow-activated carbons (HPHACs) have been prepared innovatively by pyrolyzation of setaria viridis combined with alkaline activation for the first time. The micro-morphology, pore structure, chemical compositions, and electrochemical properties are researched in detail. The obtained HPHACs are served as outstanding electrode materials in electrochemical energy storage ascribe to the particular hierarchical porous and hollow structure, and the precursor setaria viridis is advantage of eco-friendly as well as cost-effective. Electrochemical measurement results of the HPHACs electrodes exhibit not only high specific capacitance of 350 F g−1 at 0.2 A g−1, and impressive surface specific capacitance (Cs) of 49.9 μF cm−2, but also substantial rate capability of 68% retention (238 F g−1 at 10 A g−1) and good cycle stability with 99% retention over 5000 cycles at 5 A g−1 in 6 M KOH. Besides, the symmetrical supercapacitor device based on the HPHACs electrodes exhibits excellent energy density of 49.5 Wh kg−1 at power density of 175 W kg−1, but still maintains favorable energy density of 32.0 Wh kg−1 at current density of 1 A g−1 in 1-ethy-3-methylimidazolium tetrafluoroborate ( EMIMBF4) ionic liquid electrolyte, and the excellent cycle stability behaviour shows the nearly 97% ratio capacitance retention of the initial capacitance after 10,000 cycles at current density of 2 A g−1. Overall, the results indicate that HPHACs derived from setaria viridis have appealing electrochemical performances thus are promising electrode materials for supercapacitor devices and large-scale applications.

    Abstract
    1 Introduction
    2 Experiments
        2.1 Preparation of HPHACs
        2.2 Characterization of HPHACs samples
        2.3 Electrochemical measurements
    3 Results and discussion
    4 Conclusions
    Acknowledgements 
    References

• Rui Yan(Department of Materials Engineering, Taiyuan Institute of Technology, Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences)
• Kai Wang(Institute of Science and Technology, Shanxi Coal Import and Export Group Co, Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences)
• Xiaodong Tian(Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences)
• Xiao Li(Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences)
• Tao Yang(Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences)
• Xiaotong Xu(Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences)
• Yiting He(Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences)
• Shiwen Lei(Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences)
• Yan Song(Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences)