Advanced asymmetrical supercapacitors based on graphene hybrid materials

Supercapacitors operating in aqueous solutions are low cost energy storage devices with high cycling stability and fast charging and discharging capabilities, but generally suffer from low energy densities. Here, we grow Ni(OH)(2) nanoplates and RuO(2) nanoparticles on high quality graphene sheets in order to maximize the specific capacitances of these materials. We then pair up a Ni(OH)(2)/graphene electrode with a RuO(2)/graphene electrode to afford a high performance asymmetrical supercapacitor with high energy and power density operating in aqueous solutions at a voltage of similar to 1.5 V. The asymmetrical supercapacitor exhibits significantly higher energy densities than symmetrical RuO(2)-RuO(2) supercapacitors or asymmetrical supercapacitors based on either RuO(2)-carbon or Ni(OH)(2)-carbon electrode pairs. A high energy density of similar to 48 W center dot h/kg at a power density of similar to 0.23 kW/kg, and a high power density of similar to 21 kW/kg at an energy density of similar to 14 W center dot h/kg have been achieved with our Ni(OH)2/graphene and RuO(2)/graphene asymmetrical supercapacitor. Thus, pairing up metal-oxide/graphene and metal-hydroxide/graphene hybrid materials for asymmetrical supercapacitors represents a new approach to high performance energy storage.