Ideal nanoporous gold based supercapacitors with theoretical capacitance and high energy/power density

Abstract

Supercapacitors are known to suffer from relatively low energy density and stability, which hampers their substitution for existing batteries. Here, we report an outstanding positive electrode platform for supercapacitor having both high energy density and high power density as well as good stability, by fabricating a low resistance Ohmic contact between Ni(OH)2 active materials and a 3-D current collector, nanoporous gold (NPG). The Ni(OH)2/NPG electrode was optimized by finely adjusting the portion of two different parts of the deposited Ni(OH)2, one part in direct contact with the NPG and the other part on top of the NPG. The optimized Ni(OH)2/NPG electrode exhibited 2223F/cm3 of volumetric capacitance (considering both the active material and the current collector) at a current density of 5A/g, values which are beyond the theoretical capacitance value, and the device retained 90% capacitance of the initial value at 500A/g and after 30,000 cycles, respectively. This electrode showed an excellent energy density of 98Wh/kg and power density of 50kW/kg in a Ni(OH)2/NPG//MnO2/NPG two electrode supercapacitor system. The excellent performance of the Ni(OH)2/NPG electrode is attributed not only to the increased surface area of the Ni(OH)2 active materials, but also to the favorable path for charge transport created between the Ni(OH)2 and the gold electrode due to the presence of Ohmic contact, which eventually leads to the good kinetic properties and good stability.