Improving Ni(OH)2/C Supercapacitive Performances through Mixed Solvents and Thermal Treatment of XC-72

A Ni(OH)2/XC-72 nanocomposite was first synthesized via a solvothermal method in mixed solvents of ethylene glycol and H2O; using a smaller amount of ethylene glycol not only reduces the cost but also enhances the electrochemical performances of the composite. X-ray diffraction patterns indicate that α-Ni(OH)2 and β-Ni(OH)2 are coexistent in the Ni(OH)2/XC-72 composite. The capacitance of α,β-Ni(OH)2/XC-72 increases from 1649.3 F g–1 of α-Ni(OH)2/XC-72 and 1232.5 F g–1 of β-Ni(OH)2/XC-72 to 1803.1 F g–1 at 1 A g–1. To further improve the electrochemical performances of Ni(OH)2/XC-72 composite, XC-72 was calcined in an Ar flow at 600 °C (denoted as T-XC-72) to remove some oxygen-containing groups, thus increasing its electronic conductivity and also gaining more defects as nuclei for Ni(OH)2 particle deposition. The obtained Ni(OH)2/T-XC-72 composite delivers a capacitance of 2252.8 F g–1 at 1 A g–1, which is much higher than that of Ni(OH)2/XC-72. Furthermore, 78.1% of capacitance can be retained at 20 mV s–1 with respect to 74.8% of Ni(OH)2/XC-72. Additionally, it shows a stability of 80.5% over 1000 cycles at 10 A g–1, which is also more superior to 75% of Ni(OH)2/XC-72. Therefore, this work may provide a cost-effective route to synthesize high-performance electrode materials for supercapacitors.