Carbon nanotube-regulated growth of metal–organic framework nanosheets for enhanced electrochemical energy storage

Abstract

The design and synthesis of innovative two-dimensional (2D) metal–organic framework (MOF) nanosheets with superior electrochemical performance have substantial impacts on energy storage. Herein, a series of Ni-Tdc/CNT composites with excellent electrical conductivity and mechanical properties was synthesized using 2D Ni-MOFs and CNTs via a simple one-step hydrothermal process in a DMF/H₂O mixed solvent. The incorporation of CNTs mitigated the stacking phenomenon of Ni-Tdc nanosheets, facilitated the transmission of electrons within the electrode and reduced the volume deformation of the electrode material during electrochemical reactions. The unique, large-sized nanosheet structure of the Ni-Tdc/CNT composites increased accessible redox-active sites while promoting the penetration of electrolyte ions. The optimal Ni-Tdc/CNTs-20 composite (with a CNT mass fraction of 8%) obtained by modulating the mass fraction of CNT demonstrated a high specific capacity of 373.1 C g⁻¹ (757.8 F g⁻¹) at a current density of 1 A g⁻¹ and an excellent rate capacity of 79.4% retention at 10 A g⁻¹. Moreover, an asymmetric supercapacitor device composed of Ni-Tdc/CNTs-20 composite and active carbon exhibited a high energy density of 45 W h kg⁻¹ at a power density of 8000 W kg⁻¹ and an outstanding cycle life with a capacitance retention of 74.1% after 5000 cycles. This work demonstrates the enormous potential for energy storage and conversion applications by integrating 2D Ni-MOF and CNT composites.