Direct growth of hierarchical CoFe2O4 flower-like nanoflake arrays on Ni foam for high performance asymmetrical supercapacitor

Abstract

• Tulip-like iron microstructure was electrodepositied on Ni foam from suspension of Fe 2 O 3 . • Fe@Ni foam was hydrothermally converted into CoFe 2 O 4 /Ni foam in solution of Co 2+ . • Hierarchical flower-like CoFe 2 O 4 nanoflake arrays exhibits excellent electrochemical properties. • ASC assembled with CoFe 2 O 4 /Ni foam and AC demonstrates capacitive performances. Flower-like cobalt ferrite (CoFe 2 O 4 ) nanflake arrays with high mass-loading was directly grown on Ni foam with a facile two-step hydrothermal method. First, hierarchical tulip-like Fe microstructure was electrodeposited on Ni foam from an alkaline Fe 2 O 3 suspension. Then, CoFe 2 O 4 flower-like CoFe 2 O 4 nanoflake arrays on Ni foam (CoFe 2 O 4 /Ni foam) was produced by heating Fe-modified Ni foam in cobalt nitrate aqueous solution containing low concentration of copper sulfate. The CoFe 2 O 4 /Ni foam was characterized with scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-Ray spectroscopy (EDS) and Brunauer-Emmett-Teller gas sorptometry measurements (BET). The electrochemical performances of CoFe 2 O 4 /Ni foam were tested with cyclic voltammetry (CV), galvanostastic charge/discharge technique (GCD) and electrochemical impedance spectroscopy (EIS). As capacitive electrode, CoFe 2 O 4 /Ni foam exhibits high areal capacity (9.7C cm −2 at 10 mA cm −2 ), good columbic efficiency (97.25% at 10 mA cm −2 ) and excellent cycling stability (capacity retention of 89.7% after 5000 GCD cycles at 20 mA cm −2 ). Asymmetric supercapacitor, assembled with CoFe 2 O 4 /Ni foam and activated carbon (AC) as positive and negative electrodes, respectively, exhibits high energy density of 6.01 W h m −2 at energy density of 50 W m −2 , indicating the promising application prospect of CoFe 2 O 4 /Ni foam in energy storage.