High-performance solid-state supercapacitor based on Co-Ni bimetallic sulfide supported on graphene aerogel electrodes

Solid-state supercapacitors offer advantages such as higher safety and easier integration compared to their liquid electrolyte counterparts. However, it is still limited by the instability of the electrode structure and the limited capacitance storage capacity in practical applications. Herein, melamine foam (MF) was employed as a carrier for the impregnation of graphene oxide (GO) and Co²⁺, Ni²⁺ ions. By taking advantage of the porous network skeleton of MF, the electrostatic interaction between the positively charged metal ions and the negative charges of oxygen functional groups in GO, the "sea urchin-like" Ni-Co precursor encapsulated by GO was successfully created through a hydrothermal reaction. Following the carbonization and vulcanization processes, a porous NiCo₂S₄/GM aerogel loaded with uniformly dispersed NiCo₂S₄ nanoparticles was produced. The synergistic effect of the abundant active sites in NiCo₂S₄ and the large specific surface area coupled with the excellent conductivity of graphene, facilitates the rapid infiltration of electrolytes, thereby enhancing the diffusion of OH⁻ and the electron/ion transfer rate during the redox reaction between Ni²⁺/Co²⁺ ions and OH⁻. Consequently, the as-prepared NiCo₂S₄/GM electrode exhibits a high specific capacitance of up to 2515.3 F·g⁻¹ at a current density of 0.5 A·g⁻¹, along with excellent rate and cycle stability performance. Using a KOH/PVA gel electrolyte, the NiCo₂S₄/GM//AC solid-state supercapacitor achieves an energy density of 51.6 Wh∙kg⁻¹ at a power density of 814.9 W∙kg⁻¹, with a specific capacitance retention rate of 93.5% after 10,000 cycles. Hence, the as-developed graphene aerogel loaded with uniformly dispersed nano NiCo₂S₄ particles is an electrode material with excellent performance and hold promising practical application prospects.