Structurally stable hollow mesoporous graphitized carbon nanofibers embedded with NiMoO4 nanoparticles for high performance asymmetric supercapacitors

Herein, we report a facile and scalable method of synthesizing NiMoO4 nanoparticle embedded mesoporous hollow carbon nanofibers by electrospinning. We have synthesized four different NiMoO4-carbon composite nanostructures, each containing a different composition of NiMoO4 and carbon. Amongst these, the composite nanostructure with 50% (wt.) of NiMoO4 displayed an excellent specific capacity of 575 C g−1 (1438 F g−1) at 1 A g−1 current density and a capacity retention of 88% after 3000 cycles; while the pure electrospun NiMoO4 nanofibers displayed a specific capacity of 385 C g−1 (836 F g−1) and a capacity retention of only 72%. An asymmetric supercapacitor fabricated from this composite nanostructure and activated carbon displayed a high specific capacity of 135 C g−1 (85 F g−1) at 1 A g−1 and a capacity retention of 92% after 3000 cycles. A high energy density of 30 WhKg−1 and a power density of 403 WKg−1 have been achieved. The enhanced capacity of the NiMoO4-carbon composite nanofibers could be attributed to the mesoporous size of the hollow carbon nanofibers (∼3.4 nm), their high specific surface area (∼253 m2 g−1) and the increased reactivity due to the nanosized metal oxide particles. The improved cyclability can be attributed to the structural stability gained by embedment of the particles into the hollow carbon matrix that acts as a buffer during the volume changes of the cycling process. Furthermore, the encapsulation of the particles by the onion-like graphitic carbon layers prevents the particles from dislodging from the carbon matrix. The synergistic effects from NiMoO4 and carbon enhances the performance that could not be obtained by either of these components alone. These results show that these NiMoO4-carbon composite nanofibers could be promising materials for high performance supercapacitors.