Solvothermal synthesis of nanostructured nickel-based metal–organic frameworks (Ni-MOFs) with enhanced electrochemical performance for symmetric supercapacitors

Abstract

Metal–organic frameworks (MOFs) have been studied in a wide range of applications due to their high porosity, large specific surface areas and tunable structures. Nonetheless, the synthesis environment such as compositional and processing parameters has a crucial role to play in the structural and morphological properties. In this study, the impact of temperature and time on the morphology and electrochemical performance of nickel-based MOFs (Ni-MOFs) were systematically investigated. In particular, Ni-MOF nanomaterials were synthesized at different solvothermal temperature ranges: (i) 100, 120 and 140 °C (below the boiling point of DMF, ~ 153 °C); (ii) 160 and 180 °C (above the boiling point of DMF but below the boiling point of ethylene glycol (EG), ~ 197.3 °C) and (iii) 200 °C (above the boiling point of EG). Meanwhile, the solvothermal reaction time ranged from 8 to 32 h. It was found that the average size of Ni-MOF nanosheets tended to decrease with increasing solvothermal temperature. However, the crystallinity of Ni–MOF indicated a direct correlation with synthesis temperature. The solvothermal time only had a slight influence on the resultant morphologies. Noteworthily, an excellent energy density of 22.44 Wh kg⁻¹ and a superior cyclic durability of 118% over 10,000 cycles were achieved by the nanostructures synthesized at 160 °C, which has been used in the symmetrical supercapacitor electrodes in an environmental-friendly aqueous electrolyte. The results showed that such Ni-MOF nanomaterials can be used as a potential symmetrical electrode in the application of SCs.