Electro-synthesized Ni coordination supermolecular-networks-coated exfoliated graphene composite materials for high-performance asymmetric supercapacitors

Abstract

The high surface area of metal–organic frameworks (MOFs) has attracted considerable attention toward them as promising candidates for electrochemical capacitors, but their poor conductivity has limited their use in this field. Coordination supramolecular networks (CSNs) also exhibit a high specific surface area. However, they have been scarcely applied as electrode materials for supercapacitors yet. In the present study, a honeycomb-shaped Ni-pydc (pydc = pyridine-2,6-dicarboxylate) supermolecular-networks-coated electrochemically exfoliated graphene (Ni-pydc@EEG) composite was synthesized via a simple one-step electrochemical synthesis. The capacitance of the Ni-pydc@EEG composite increased sharply up to 835.3 F g⁻¹ at 5 A g⁻¹, while the pure Ni-pydc supermolecular networks could store only 158.7 F g⁻¹ and the pure EEG could achieve only about 193.6 F g⁻¹. This high capacitive performance could be attributed to the electrochemical synergistic effect between the redox active Ni-pydc and the EEG. To test for practical application, a small solid-state asymmetric device (Ni-pydc@EEG//EEG) was assembled and achieved a considerable energy density of 14.5 W h kg⁻¹ at a high power density of 7500 W kg⁻¹ and the ability to power a 2.5 W fan motor directly. The present work illustrates the magnificent potential of coordination supermolecular networks in electrochemical energy storage applications.