Electrospun Mesoporous NiZnFeO - CNT - Hollow Carbon Ternary Composite Nanofibers as High Performance Electrodes for Advanced Symmetric Supercapacitors.

Spinel ferrites have attracted considerable interest in energy storage systems due to their unique magnetic, electrical and catalytic properties. However, they suffer from poor electronic conductivity and low specific capacity. We have addressed this limitation by synthesizing composite hollow carbon nanofibers (HCNF) embedded with nanostructured Nickel Zinc Ferrite (NZF) and Multiwalled carbon nanotubes (CNT), through coaxial electrospinning. These ternary composite nanofibers NZF-CNT-HCNF have a high specific capacity of 833 C g at a current density of 1 A g and have a capacity retention of 90 % after 3000 cycles. Their performance is much better than pure NZF fibers (180 C g) or hollow carbon nanofibers (96 C g), suggesting synergy between various constituents of the composite. A symmetric supercapacitor fabricated from NZF-CNT-HCNF composite nanofibers (30 % NZF) has a high specific capacity of 302 C g (302 A g) at a current density of 1 A g and has a capacity retention of 95 % after 5000 cycles. At the same current density, the device has a high energy density of 39 Whkg and power density of 1000 Wkg at a current density of 1 A g. This performance can be attributed to the high specific surface area (776 m g), mesoporosity (pore size ~4 nm), interconnectedness of the nanofibers and high electrical conductivity of CNTs. These fibers can be used as light-weight high performance electrode materials in advanced energy storage devices.