Interconnected CoNi-Se Hollow Flakes through Reduced Graphene Oxide Sheets as a Cathode Material for Hybrid Supercapacitors.

Achieving a high energy density and long-cycle stability in energy storage devices demands competent electrochemical performance, often contingent on the innovative structural design of materials under investigation. This study explores the potential of transition metal selenide (TMSe), known for its remarkable activity, electronic conductivity, and stability in energy storage and conversion applications. The innovation lies in constructing hollow structures of binary metal selenide (CoNi-Se) at the surface of reduced graphene oxide (rGO) arranged in a three-dimensional (3D) morphology (CoNi-Se/rGO). The 3D interconnected rGO architecture works as a microcurrent collector, while porous CoNi-Se sheets originate the active redox centers. Electrochemical analysis of CoNi-Se/rGO based-electrode reveals a distinct faradic behavior, thereby resulting in a specific capacitance of 2957 F g-1 (1478.5 C g-1), surpassing the bare CoNi-Se with a value of 2149 F g-1 (1074.5 C g-1) at a current density of 1 A g-1. Both materials exhibit exceptional high-rate capabilities, retaining 83% of capacitance at 10 A g-1 compared to 1 A g-1. In a two-electrode coin cell system, the device achieves a high energy density of 73 Wh kg-1 at a power density of 1500 W kg-1, stating an impressive 90.4% capacitance retention even after enduring 20,000 cycles. This study underscores the CoNi-Se/rGO composite's promise as a superior electrode material for high-performance energy storage applications.