Controllable synthesis of 3D binary nickel-cobalt hydroxide/graphene/nickel foam as a binder-free electrode for high-performance supercapacitors

Binder-free electrodes based on 3D porous nickel-cobalt binary hydroxides (NCH)/graphene (G) composites on nickel foam (NF) for supercapacitors are fabricated via a chemical vapor deposition (CVD) process combined with an electrochemical deposition (ED) method. High quality graphene grown on NF makes the surface more suitable for deposition of 3D porous NCH and simultaneously enhances the electrode conductivity. The 3D structure can improve the electron transport ability and increase the contact of the active sites with electrolyte. The morphology and electrochemical performance of NCH/G/NF electrodes can be readily manipulated by adjusting the deposition current density and the Ni-Co ratio of the deposition solution. High capacitance with enhanced stability and rate capability is achieved and is attributed to the synergetic effect of the above factors. Specifically, at the deposition current density of 0.625 mA cm(-2) and Ni-Co ratio of 1 : 1, the NCH11/G/NF electrode exhibits a maximum specific capacitance of 1410 F g(-1) at 2 A g(-1). When the current density increases to 4 A g(-1), the capacitance is still 1328 F g(-1) with a high capacitance retention of 94.2%. After 2500 cycles, the capacitance retention is 92.1%, which is higher than that of a common slurry-coated electrode. To research its practical applications, an asymmetric supercapacitor was fabricated with a NCH11/G/NF electrode as the positive electrode and activated carbon as the negative electrode. The asymmetric device exhibits a prominent energy density of 33.75 W h kg(-1) at a power density of 750 W kg(-1). The binder-free electrode with superior performance has been proven to be very promising for energy storage.