Rationally constructing a hierarchical two-dimensional NiCo metal–organic framework/graphene hybrid for highly efficient Li⁺ ion storage

Abstract

Recently, metal-organic frameworks (MOFs) have been used to synthesize electrode materials such as porous carbon, metal oxides, and metal chalcogenides or directly utilized as electrodes. However, pristine MOF electrodes suffer from problems such as unstable structures and low electronic conductivity. Herein, we rationally construct a hierarchical two dimensional (2D) bimetallic NiCo MOF-graphene (NiCo MOF-G) hybrid through a facile solution reaction. The ultrathin bimetallic MOF nanosheets are directly anchored on the graphene sheets in a mixture solution of NiCl2, CoCl2, and benzendicarboxylic (BDC) acid. The -COOH groups in BDC2- can chelate with both Ni2+/Co2+ and graphene sheets to form a stable 2D NiCo MOF-G hybrid. The NiCo MOF-G electrode can provide shortened pathways for charge transport and a stable conjugated aromatic structure, showing good cycling stability. The graphene nanosheets can enhance its conductivity and structural stability, thus enhancing its electrochemical performances. The Li+ insertion/extraction mechanism of this NiCo MOF-G hybrid is studied in depth through potentiodynamic electrochemical impedance spectroscopy, ex situ scanning electron microscopy, and X-ray photoelectron spectroscopy. Attributed to these advantages, the 2D NiCo MOF-G hybrid demonstrates an exceptional capacity of 640 mA h g-1 at 1 A g-1 over 500 cycles and an excellent rate capability of 424 mA h g-1 at 3 A g-1.