Morphology control of nanoscale metal-organic frameworks for high-performance supercapacitors

Abstract Metal-organic frameworks (MOFs) as a promising electrode materials have received increasing attention in supercapacitors. The construction of nanoscale MOF materials was considered as an effective strategy to enhance electrochemical performances. In this work, CuMOF crystal and NiMOF crystal are synthesized by selecting redox-active organic linker and metal centers. Then, an in-situ solvothermal method is developed and applied successfully to prepare their nano materials, named as nano-CuMOF 1–10 and nano-NiMOF 1–10, under a facile and mild condition. In particular, it is found that various morphology and nano sizes for these nano-CuMOFs and nano-NiMOFs can be effectively controlled based on solvent effect and surfactant effect. All structures of as-synthesized nano materials are demonstrated by XRD and FT-IR results, which are consistent with the ones of their crystals. More importantly, electrochemical properties can be greatly enhanced from bulk crystals of CuMOF and NiMOF to nano-CuMOF and nano-NiMOF materials. Their nano materials exhibit excellent supercapacitor performance. Among of them, nano-NiMOF 3 as supercapacitor electrode shows the best specific capacitance of 1024.44 F g−1 at a current densities of 1 A g−1 and maintains very good cycling stability. Its capacitance retention of 49.07% can be observed after 5000 cycles at a current density of 5 A g−1. In addition, a high-performance asymmetric supercapacitor (ASC) was fabricated by using nano-NiMOF 3 and activated carbon as two electrodes. A specific capacitance of 38.65 F g−1 was obtained at a current density of 0.5 A g−1, and 109% capacity of the initial capacitance at 3 A g−1 after 5000 cycles can be observed.