Hierarchically porous CoFe2O4 nanosheets supported on Ni foam with excellent electrochemical properties for asymmetric supercapacitors

A new type of hierarchically mesoporous cobalt ferrite oxide nanosheets, CoFe2O4 nanosheets, has been successfully fabricated via a simple hydrothermal method on the Ni foam followed by a post-annealing treatment. This CoFe2O4 nanosheets was employed as a supercapacitor electrode and exhibited an excellent capacitance of 503 F g(-1) at a current density of 2 A g(-1). When the current density increased to 20 A g-1, the capacitance of CoFe2O4 nanosheets can maintain 78.5% (395 F g(-1)) of the initial value, indicating the remarkable rate capability of the as-prepared CoFe2O4 nanosheets. An aqueous asymmetric supercapacitor (ASC) based on CoFe2O4 nanosheets as a positive electrode and the activated carbon (AC) as a negative electrode was assembled for the first time. The as-fabricated ASC delivered a specific capacitance of 73.12 F g(-1) at a current density of 1.2 A g(-1) in a voltage window of 1.5 V. The CoFe2O4//AC ASC could achieve a high energy density of 22.85 Wh kg(-1) and good long-term cycling stability (98% retention after 5000 cycles). These results demonstrated that CoFe2O4 nanosheets could be one of the promising electrode material for supercapacitors applications. (C) 2017 Elsevier B.V. All rights reserved.