Enhanced energy storage ability of UIO66 active material on acid-treated carbon cloth for flexible supercapacitors

Effect of Sulfur Vacancies of CoNi2S4 on Its Electrochemical Performance in Hybrid Supercapacitors

Ternary cobalt nickel sulfides are considered promising electrode materials due to their unique physical properties. However, its capacitive performance is still limited by the insufficient material utilization efficiency. Here, we design and fabricate CoNi2S4 with nanorods and hairy-petal-like nanosheets on nickel foam (NF) as an excellent self-standing electrode for a hybrid supercapacitor (HSC). The CoNi2S4 electrode material was synthesized on the NF substrate by cobalt organic framework (Co-MOF) conversion and introducing sulfur ion and nickel ion exchange. The CoNi2S4 electrode material with sulfur vacancies was controlled by regulating the reduction time, and then electrochemical analysis and comparison were performed. The results demonstrate that the synergistic effect of the MOF-derived CoNi2S4 skeleton and sulfur vacancies can significantly improve the electrochemical activity of nickel cobalt sulfide. The CoNi2S4 electrode exhibits a superior high specific capacitance of 5.24 F/cm2 at a current density of 3 mA/cm2. Furthermore, the assembled CoNi2S4-60//AC HSC displays a high energy density of 59.41 Wh/kg and a power density of 999.98 W/kg. Even after 10,000 continuous charge-discharge cycles, its initial capacitance was retained at 89.24%. These results demonstrate the feasibility and practicality of CoNi2S4-60 as an electrode material, showcasing its potential for real-world applications.

Novel In Situ Synthesis of Freestanding Carbonized ZIF67/Polymer Nanofiber Electrodes for Supercapacitors via Electrospinning and Pyrolysis Techniques

Zeolitic imidazolate framework-67 (ZIF67) has been regarded as an effective energy storage material due to its high surface area and electroactive cobalt center. Carbonizing ZIF67 can enhance electrical conductivity by converting 2-methylimidazole (2-melm) to carbon with cobalt doping. In this work, a novel in situ electrospinning is proposed to fabricate carbonized ZIF67 on carbon fiber (C67@PAN-OC) as a freestanding supercapacitor electrode. Polyacrylonitrile solution containing a cobalt precursor is used for electrospinning, and produced fibers are immersed in 2-melm to form ZIF67. Individually grown carbonized ZIF67 on carbon fiber is obtained using the in situ electrospinning method, while the one-body mixed carbon electrode is formed using the ex situ electrospinning method. A highest specific capacitance (C_F) of 386.3 F/g at 20 mV/s is obtained for the in situ synthesized C67@PAN-OC electrode due to the largest electrochemical surface area and the smallest resistance, while the ex situ synthesized electrode only shows a C_F value of 27.7 F/g. A symmetric supercapacitor (SSC) assembled using the optimized C67@PAN-OC electrodes and gel electrolytes shows a maximum energy density of 9.64 kWh/kg at 0.55 kW/kg and a C_F retention of 59.5% after 1000 times charge/discharge process. A C_F retention of 75.6% after bending 100 times is also obtained for SSC.