Metal-organic framework-derived carbon-cobalt oxysulfide nanocage heterostructure electrode for efficient hybrid supercapacitors

Construction of hybrid supercapacitors (HSCs) with defect engineered electrodes derived from single metal-organic frameworks (zeolitic imidazolate frameworks, ZIF-67) via control of the thermal influences showed unique structural features and rich electrochemical properties. Designing the three-dimensional Co oxysulfide nanograins with carbon frame (CoOS-C)-based positive electrode surfaces through sulfidation with tunable defect states along with N- and S-doping states improved the electrical energy storage; further, the possibility of having a carbon-based skeleton surface influenced the effective rate capability during the charge-discharge process. This unique nanostructural feature with encapsulation of porous N- and S-doped graphitic carbon enabled improved rate performance by enhancing the stability of the electrode material and shortening the ion-diffusion paths by the synergistic effect. Owing to the tunable defect functionality, the CoOS-C based electrode exhibited a high storage capacity of 708.8 C g⁻¹ at 1 A g⁻¹ and an excellent rate capability with long-term cyclic stability, with more than 93% capacity retention after 3000 cycles. Furthermore, the fabricated HSCs operated within a wide potential window of 1 to 1.6 V, which allowed excellent rate capability with a high-energy density of 31.7 W h kg⁻¹ at a specific power density of 800 W kg⁻¹ with long-term cyclic stability up to 10 000 cycles.