MOF-derived NiO/Ni architecture encapsulated into N-doped carbon nanotubes for advanced asymmetric supercapacitors

Abstract

Metal–organic frameworks (MOFs) are promising precursors for the construction of various functional materials for high-performance electrochemical energy storage devices. Herein, we introduce a novel strategy for the synthesis of NiO/Ni architecture encapsulated into N-doped carbon nanotubes (NiO/Ni/NCNTs) through a simple two-step method. First, 3D columnar nickel-based MOFs (Ni-MOFs) were synthesized via a solution reaction. Then the Ni²⁺ in Ni-MOFs was partly reduced to Ni to catalyze the formation of NCNTs through an inert atmosphere calcination treatment. These NiO/Ni/NCNTs nano-composites can not only provide more reactive sites for electrochemical reactions, but also provide conductive channels for electron transport. They exhibit a specific capacitance of 777.5 F g⁻¹ at 1 A g⁻¹ in a three-electrode system. An asymmetric supercapacitor is assembled using NiO/Ni/NCNTs as the anode electrode and porous carbon as the cathode electrode, which has demonstrated an energy density of 33.89 W h kg⁻¹ at a power density of 800 W kg⁻¹ and excellent cycling performance (capacitance retention is nearly 90% at a current density of 1 A g⁻¹ after 40 000 cycles). The NiO/Ni/NCNTs will become a great potential electrode material for supercapacitors.