CoFe₂O₄ Hollow Spheres-Decorated Three-Dimensional rGO Sponge for Highly Efficient Electrochemical Charge Storage Devices

The energy demand, the crisis of fossil fuels, and the increasing popularity of portable and wearable electronics in the global market have triggered the demand to develop high-performance flexible all-solid-state supercapacitors that are capable of delivering high energy at high power density as well as being safely entrenched in those electronics. Herein, we have designed a nanocomposite, 80CF_hs-20rGO_sp, which exhibits a high specific capacitance (C_S) value of 1032 F g^–1 at 3 A g^–1. Utilizing this nanocomposite as the cathode and reduced graphene oxide sponge (rGO_sp) as the anode, a flexible all-solid-state asymmetric device has been fabricated. In this device, poly­(vinyl alcohol) (PVA) gel embedded with a mixture of 3 M KOH and 0.1 M K₄[Fe­(CN)₆] was used as an electrolyte cum separator. The fabricated device showed the capability to deliver an energy density of 65.8 W h kg^–1 at a power density of 1500 W kg^–1 and retained its capability even after various physical deformations. The device also exhibited a long cycle life and retained ∼96% of its C_S value after 5000 cycles. Moreover, the fabricated flexible all-solid-state device successfully illuminated light-emitting diodes, which proved its potential use in real-life supercapacitor applications. The obtained results revealed the excellent electrochemical performances of the fabricated device and rendered it a promising candidate in the energy sector.