Cobalt carbonate hydroxide-embedded in multi-layered holey nanoflower cross-linked with carbon nanotube for highly efficient supercapacitors with ultrahigh rate performance

In this work, bimetallic nickel-cobalt based metal organic framework (MOF) is in-situ grown on 2D laminar Co2(OH)2CO3 with multi-walled carbon nanotubes (MWCNTs) aid to form nanoflower-like hierarchical porous heterogeneous structure for advanced supercapacitor application. Benefitting from the low crystal surface energy of Co2(OH)2CO3, its intersection and connection with MOF generate convenient electron path and open channel for ionic transmission, and large contact area. The high aromaticity of MWCNTs slows down destruction for MOF structure from water molecule through providing hydrophobic environment, guaranteeing stable presence of the resulting composite in aqueous electrolyte. The synergistic effect of Ni/Co with high redox activity in bimetallic NiCo-MOF provides rapid and multiple redox reactions for enhanced capacitance. Taking full advantage of promising merits of individual components, the optimized NiCo MOF-Co2(OH)2CO3 nanosheet-MWCNT30 (NCMNS-CNT30) composite under MWCNT dosage of 30 mg delivers greatly enhanced specific capacitance (1773 F g-1 at 1 A g-1) and obviously improved rate performance (96.5 % retention at 10 A g-1). Based on it, the fabricated hybrid supercapacitor (HSC) NCM-NS-CNT30//AC presents comparatively good energy density (30.625 Wh Kg-1), superior to most recently reported Ni, Co-based supercapacitors.