Electrosynthesis of semitransparent Ni-Co₂-Cu_x mixed oxide electrode film for novel solid state asymmetric planar supercapattery application

Herein, we have successfully grown transparent NiCo₂ and Cu mixed oxide thin film electrode material by a facile electrodeposition process from electrolyte containing hydrated salts of its composite metals at two different temperatures. Microstructural and some other surface studies were carried out with the aid of suitable and appropriate probing facilities such as scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffractometer (XRD), Raman microscope and ultraviolet-visible spectrophotometer. Microstructural studies on the samples revealed the formation of seed flowerlike nanosheet by the film grown from room temperature electrolyte which was found to become porously stacked and agglomerated as observed for the one grown at higher temperature. Further probing showed that the grown film exhibit crystallinity and surface roughness of high degree. Optical energy band gap values were also found to be 3.08 and 3.00 eV depending on the synthesis protocols observed. The optimum electrode sample exhibited high specific capacitance and capacity of 1940.1 Fg⁻¹ and 134.2 mAhg⁻¹, respectively and with excellent cycling stability when tested as half-cell in three-electrode mode and 1 M aqueous KOH electrolyte. It was further utilized as positrode in a fabricated solid state asymmetric supercapattery device with reduced graphene oxide (RGO) as negatrode and powdered PVA-KOH electrolyte. The device displayed intriguing performance having demonstrated excellent cycling in high voltage (0 to 1.6 V) window and over 20,000 charge-discharge cycles, and with high areal capacitance, energy density and power density of 20.2 mFcm⁻², 25.60 Whcm⁻² and 2344.42 Wcm⁻², respectively. The study demonstrated the significant supercapacitive potentials of the fabricated electrode material for high quality energy storage devices.