Asymmetric supercapacitors (ASCs) based on pseudocapacitor electrode materials are vital to improve the electrochemical properties of devices in aqueous electrolytes. This study fabricates hollow N-doped carbon sphere (h-NCS) to produce h-NCS@PANI nanocomposite as positive electrode and alpha-MoO3 as negative electrode to assemble ASC device. In particular, a facile template-free synthesis method, catalyzed by Cu2+, is used to prepare hollow PANI nanosphere precursor to build h-NCS. The mechanism of the precursor formation is illustrated in detail. After polymerization of PANI on the surface of h-NCS, the capacitance increases to 327 F g(-1) at 1 A g(-1). Furthermore, a hydrothermal reaction is carried out to produce a-MoO3 negative electrode material. The maximum specific capacitance of 720 F g(-1) is achieved at 1 A g(-1). The obtained h-NCS@PANI and a-MoO3 are utilized to construct an ASC device. The electrochemical properties of this device are investigated comprehensively. The maximum energy density of 34.1Wh kg(-1) and power density of 9350.6 W kg(-1) are observed, which provide an insight into the development of ASCs. (C) 2018 Elsevier B.V. All rights reserved.