Design of Co_0.85Se Microsphere-like Architectures for High-Performance Hybrid Supercapacitors

This study presents the synthesis of Co_0.85Se microsphere-like structures on nickel foam (NF) substrates for high-performance HSC applications. The Co_0.85Se microspheres were synthesized using a two-step hydrothermal process, yielding well-distributed—albeit non-uniform—structures on the NF substrate. The electrochemical performance of the Co_0.85Se/NF electrode, evaluated in a three-electrode system, demonstrated remarkable characteristics, including a high specific capacity of 719 C g⁻¹ at 1 A g⁻¹ and outstanding long-term cycling stability, with 87.1% capacity retention over 10,000 charge-discharge cycles. To assess the practical applicability of the Co_0.85Se/NF electrode, a hybrid supercapacitor device was assembled using activated carbon (AC) as the negative electrode and Co_0.85Se/NF as the positive electrode. The Co_0.85Se/NF//AC HSC device exhibited remarkable electrochemical performance, achieving a high energy density of 66.6 Wh kg⁻¹ at a power density of 849.3 W kg⁻¹. It also maintained excellent cycling stability over 10,000 charge-discharge cycles. These findings highlight the significant potential of Co_0.85Se microsphere-like structures as high-performance electrode materials for hybrid supercapacitors, paving the way for developing efficient energy storage technologies.