The surface modification of NiO@NiSe2 enhanced high energy storage properties for flexible hybrid supercapacitor

Abstract

Self-standing composite nanostructures have attracted significant attention in energy storage devices to enhance capacity for practical applications, such as supercapacitors. In this regard, we propose a simple and efficient electrodeposition technique to fabricate a surface-modified NiO@NiSe₂ cathode for a hybrid supercapacitor (HSC) via a chronoamperometry-based process. The composite NiO@NiSe₂ structure exhibits a high areal capacity (307.2 µAh cm⁻²) compared with NiSe₂ (213.3 µAh cm⁻²) and NiO (60.1 µAh cm⁻²) electrode materials. The enhanced performance is attributed to the smoothing effect produced by oxygen vacancies in NiO within the layered NiSe₂ nanostructure, which shortens the ion migration path, while the open structure of layered pores and nanoflakes accelerates ion transport. Furthermore, the composite NiO@NiSe₂ has been used to construct a full-cell device to demonstrate practical applicability, with activated carbon as the negative electrode material. The fabricated device, NiO@NiSe₂//AC, delivers a notable areal capacitance, energy, and power density (301.4 mF cm⁻²; 94.2 µWh cm⁻²; and 1000 µW cm⁻², respectively) at a current density of 3 mA cm⁻². Additionally, the device exhibits long-term cycling performance, maintaining 81.3 % capacity retention after approximately 4500 cycles at a practical high current density of 35 mA cm⁻². Moreover, the HSC device was successfully evaluated by powering multiple LEDs, demonstrating its practical applicability. TOF-SIMS, XPS, Raman, FE-SEM, and FE-TEM analyses were conducted to elucidate the structural evolution and electrochemical reaction mechanisms of the NiO@NiSe₂ composite structure. These results suggest that the composite structure design, including the use of activated carbon in hybrid supercapacitors, is promising for developing energy storage devices for wearable and electronic applications.