Inside-outside OH incursion involved in the fabrication of hierarchical nanoflake assembled three-dimensional flower-like α-Co(OH) for use in high-performance aqueous symmetric supercapacitor applications.

Introduction: The energy industry has been challenged by the current high population and high energy consumption, forcing the development of effective and efficient supercapacitor devices. The crucial issues until now have been high production cost, deprived cyclic stability, and squat energy density. To resolve these problems, various approaches have been taken, such as the development of long-life electrode materials with high capacity, rapid charging, and slow discharging to overcome poor life cycle stability.

Objectives: In the present work we focus on fabricating cost-effective unique-morphology, high-surface-area alpha-Co(OH) for application in an aqueous-electrolyte symmetric supercapacitor.

Methods: In this study, hierarchical nanoflakes assembled in three-dimensional (3D) flower-shaped cobalt hydroxide (HN-3DF-α-Co(OH)) electrode were synthesized using the solvothermal method with sodium dodecylbenzene sulfonate (SDBS) and methanol as solvents. Spectroscopic and microscopic techniques were used to characterize fabricated HN-3DF-Co(OH), which revealed that the materials electrode exhibited the alpha phase with a hierarchical flower-like structure. A half-cell electrochemical assembly (three-electrode assemble cell) and symmetric full cell (two-electrode assemble cell) were examined in an aqueous electrolyte.

Results: In three-electrode assembly cells, HN-3DF-α-Co(OH) exhibited 719.5 Fg specific capacitance (C) at 1 Ag with excellent cyclic retention stability of approximately 88% after 3000 cycles. In two-electrode symmetric supercapacitive systems, HN-3DF-α-Co(OH) achieved a maximum C of 70.3 Fg at 0.4 Ag with the highest energy density of approximately 6.25 Wh/kg at a power density of 328.94 W/kg. The fabricated two-electrode assembly cell with the HN-3DF-α-Co(OH) electrode retained cyclic stability of approximately 85% after 5000 repeated charge and discharge cycles.

Conclusion: Solvothermally-synthesized, optimized HN-3DF-α-Co(OH) showed outstanding electrochemical performance results in three- and two-electrode systems. This unique aqueous symmetric supercapacitor can be used to design cost-effective symmetric capacitors based on metal hydroxide.