Interface polarization matters: Enhancing supercapacitor performance of spinel NiCo2O4 nanowires by reduced graphene oxide coating

Abstract

Supercapacitors show ultrafast charging-discharging rates but extremely high powers that can address emerging energy needs, in particular for the high specific power and portable energy conversion/storage devices. Herein, we report a novel hybrid electrode material based on complementary components of NiCo2O4 nanowires and reduced graphene oxide (rGO) for high performance supercapacitor application by combining capacitive and faradaic materials and storage mechanisms. The unique heterostructured rGO/NiCo2O4 nanostructures exhibit high specific capacitance (up to 4.37 F cm−2 (1248 F g−1), measured at the current density of 2 mA cm−2 with loading of active materials 3.5 mg cm−2) and excellent cycling stability with capacitance retention of 90% after 2000 charge-discharge cycles as well as high rate capability. Due to the difference of work function, the interfacial polarization not only allow the effective adsorption/desorption of the electrolyte ions at the surface of rGO to improve electrochemical double-layer capacitance (EDLC), but also provide both electrolyte ions storage site and transport pathway to facilitate the Faradaic redox reactions near the surface of NiCo2O4. The encouraging results show that such hybrid nanostructure combining capacitive and faradaic materials and storage mechanisms have great potential in developing high performance electrochemical supercapacitors.