Metal Precursor Dependent Synthesis of NiFe2O4 Thin Films for High-Performance Flexible Symmetric Supercapacitor

Herein, we report the chemical synthesis of NiFe2O4 thin films forming nanosheet-, nanoflower-, and nanofeather-like morphologies using NiCl2. 6H(2)O, Ni(NO3)(2).6H(2)O, and NiSO4.6H(2)O nickel salt precursors, respectively, while using the same iron salt precursor. A nanostructure formation mechanism is proposed in detail using coordination chemistry theory. Interestingly, nanostructures of NiFe2O4 nanosheets revealed a maximum surface area of 47 m(2) g(-1), which was higher than those of nanoflowers and nanofeathers (25 and 11 m(2) g(-1)). Similarly, the supercapacitive properties of the individual NiFe2O4 nanosheet-based electrode demonstrated maximum specific capacitance of 1139 F g(-1), which is found to be better than that of NiFe2O4 nanoflowers (677 F g(-1)) and nanofeathers (435 F CI) in 6 M KOH electrolyte. Furthermore, the symmetric device fabricated using NiFe2O4 nanosheet electrodes and PVA-KOH solid gel electrolyte shows higher specific capacitance of 236 F g(-1) with 98% retention after 7000 cycles and higher specific energy density of 47 Wh kg(-1) at a specific power of 333 W kg(-1).