NiF₂ Nanorod Arrays for Supercapattery Applications

A electrode for energy storage cells is possible directly on Ni foam, using a simple reduction process to form NiF₂ nanorod arrays (NA). We demonstrate NiF₂@Ni NA for a symmetric electrochemical supercapattery electrode. With an areal specific capacitance of 51 F cm^-2 at 0.25 mA cm^-2 current density and 94% cycling stability, a NiF₂@Ni electrode can exhibit supercapattery behavior, a combination of supercapacitor and battery-like redox. The symmetric electrochemical supercapattery delivers 31 W h m^-2 energy density and 797 W m^-2 power density with 83% retention in a 1 M KOH electrolyte, constituting a step toward manufacturing a laboratory-scale energy storage device based on metal halides. Producing self-grown hierarchically porous nanostructured electrodes on three-dimensional metal foams by displacement reactions may be useful for other metal halides as electrodes for supercapacitors, supercapatteries, and lithium-ion batteries.