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3-D ZnFe2O4/FSSM-300 nano-flakes on flexible stainless steel mesh as anode and Ni(OH)2/FSSM-300 as cathode was used to fabricate an asymmetric supercapacitor.

Heterostructure-based metal oxide thin films are recognized as the leading material for new generation, high-performance, stable, and flexible supercapacitors. However, morphologies, like nanoflakes, nanotubes, nanorods, and so forth, have been found to suffer from issues related to poor cycle stability and energy density. Thus, to circumvent these problems, herein, we have developed a low-cost, high surface area, and environmentally benign self-assembled ZnFeO nanoflake@ZnFeO/C nanoparticle heterostructure electrode via anchoring ZnFeO and carbon nanoparticles using an in situ biomediated green rotational chemical bath deposition approach for the first time. The synthesized ZnFeO nanoflake@ZnFeO/C nanoparticle heterostructure thin films demonstrate an excellent specific capacitance of 1884 F g at a current density of 5 mA cm. Additionally, all solid-state flexible asymmetric supercapacitor devices were designed on the basis of ZnFeO nanoflake@ZnFeO/C nanoparticle heterostructures as the negative electrode and reduced graphene oxide and energy density of 81 Wh kg at a power density of 3.9 kW kg. Similarly, the asymmetric device exhibits ultralong cycle stability of 35 000 cycles by losing only 2% capacitance. The excellent performance of the device is attributed to the self-assembled organization of the heterostructures. Moreover, the in situ biomediated green strategy is also applicable for the synthesis of other metal oxide and carbon-based heterostructure electrodes.

Herein, we are reporting a simple, economic, easy to handle, scalable and reproducible mechanochemical i.e. rotational chemical bath deposition (R-CBD) approach for synthesis of well adhered nano-flakes ZnFe2O4 thin films (NFs-ZnFe2O4) with uniform morphology on stainless steel (SS) substrate, in comparison with nano-grain ZnFe2O4 thin films (NGs-ZnFe2O4) prepared using conventional CBD approach. The influence of rotation on the evolution of nano-flakes morphology in NFs-ZnFe2O4 is also investigated. The porous NFs-ZnFe2O4 thin films demonstrated excellent pseudocapacitor properties with higher specific capacitance 768 Fg -1 at high current density 5 mA cm -2 , stability upto 5000 cycles (88% retention), higher energy density (106 Wh kg -1 ) and power density (18 kW kg -1 ) compared to NGs-ZnFe2O4. The results were also found to be higher than those reported earlier for MFe2O4 based systems.