Synergistic Effect of the Graphene/NiO-β-Ni(OH)₂-CuO Cathode and the rGO/NiO-V₂O₅ Anode for Asymmetric Supercapacitors

In the present work, we focus on developing highly active materials for flexible solid-state symmetric and asymmetric supercapacitors, with the aim of enhancing their electrochemical performance. Herein, the heterostructure Graphene/NiO-β-Ni(OH)2-CuO nanocomposite is hydrothermally synthesized as a positive electrode, while the rGO/NiO-V2O5 nanocomposite is fabricated as a negative electrode in asymmetric supercapacitor applications. Structural and compositional characterization confirms that the fabricated ASC device based on Gr/NiO–β-Ni(OH)2–CuO//rGO/NiO–V2O5 is an electroactive material that benefits from oxygen vacancies generated through multiple oxidation phases. The Gr/NiO-β-Ni(OH)2-CuO composite demonstrates a remarkable areal capacitance of 3.2 F cm–2 at 3 mA cm–2. A solid-state symmetric supercapacitor (SSC) device, constructed as Gr/NiO-β-Ni(OH)2-CuO//Gr/NiO-β-Ni(OH)2-CuO (GNNC//GNNC), achieves a high energy density of 100.4 mWh cm–2 and a power density of 7200 mW cm–2 with an exceptional capacitance retention of 72.6% after 7000 cycles. The good designing of the Gr/NiO-β-Ni(OH)2-CuO//rGO/NiO-V2O5 heterostructure ASC device, with interconnected graphene sheets, can provide uniform mesoporous morphological features to facilitate the diffusion of the electrolyte and electron transfer kinetics. Furthermore, an asymmetric supercapacitor (ASC) device, assembled as Gr/NiO-β-Ni(OH)2-CuO//rGO/NiO-V2O5 (GNNC//rGNV), delivers an areal capacitance of 245.3 mF cm–2 at 1 mA cm–2, showcasing excellent rate capabilities. The ASC device also exhibits a maximum energy density of 122.6 mWh cm–2 and a power density of 4500 mW cm–2, along with an impressive capacity retention of 77.3% and a Coulombic efficiency of 93.9% at 3 mA cm–2 after 5000 cycles. The practical feasibility of the GNNC//rGNV ASC devices was evaluated by connecting them in series to power orange, blue, and red light-emitting diodes (LEDs), demonstrating their capability for real-world energy storage applications. This work underscores the significance of heterostructure nanocomposites in advancing the performance of next-generation supercapacitors, offering a promising pathway for high-energy-density and high-power-density energy storage systems.