A controllable preparation of two-dimensional cobalt oxalate-based nanostructured sheets for electrochemical energy storage

Well-defined two-dimensional(2D)cobalt oxalate(CoC_(2)O_(4)·2H_(2)O)nanosheets exhibit more excellent property than common bulk cobalt oxalate due to high specific surface areas and high-efficient transport of ion and electron.However,the delicate control of the 2D morphology of CoC_(2)O_(4)·2H_(2)O during their synthesis remains challenging.Herein,2D CoC_(2)O_(4)·2H_(2)O nanosheets(M1),grown by straightforward chemical precipitation,can be tuned from three-dimensional(3D)structure during their synthesis with no templates or capping agents.This control is obtained by rationally changing the ratio of reactants with ethylene glycol as solvent.Moreover,Co_(3)O_(4)/CoC_(2)O_(4)composites(M1-250)have been fabricated through low-temperature thermal treatment of the M1 precursor in air,which possess porous surfaces with the 2D morphology maintained.Benefiting from the porous surfaces,more redox-active sites and better electrical conductivity of Co_(3)O_(4),the constructed M1-250//AC aqueous device manifest improved kinetics of the electrochemistry process with energy density of 27.9 Wh/kg at 550.7 W/kg and good cycling stability with sustaining 73.0 m Ah/g after 5000 cycles.