Structurally Stable Mesoporous Hierarchical NiMoO4 Hollow Nanofibers for Asymmetric Supercapacitors with Enhanced Capacity and Improved Cycling Stability

Herein, we report, for the first time, the facile synthesis of four different mesoporous hierarchical structures of NiMoO4 through electrospinning: solid nanofibers, porous nanofibers, hollow nanofibers, and microplates of NiMoO4. All of these structures were investigated as electrode materials for supercapacitors. Amongst these, hollow NiMoO4 nanofibers demonstrated superior electrochemical performance with a high specific capacity of 214 mAhg(-1) (1920 Fg(-1)) at a current density of 2 Ag-1 and a capacity retention of 92% after 3000 cycles. An asymmetric supercapacitor fabricated from a hollow NiMoO4 nanofiber cathode and an activated carbon anode displayed a high specific capacity of 49 mAhg(-1) (110 Fg(-1)) at a current density of 1 Ag-1 and a capacity retention of 97% after 5000 cycles. At this current density, the device delivered a high energy density of 39 Wh Kg(-1) and a power density of 798 WKg(-1) at a relatively high mass loading of 5 mg cm(-2) of active material on the substrate. This impressive performance of hollow NiMoO4 nanofibers could be attributed to their mesoporous surface with high specific surface area (ca. 105 m(2)g(-1)), the hollow core and the interconnectedness of the fibers that improve the electrolyte penetration, increase the rate of the surface redox reactions and allow for faster transport of the charges.