Fabrication of high energy density supercapacitor device based on hollow iridium oxide nanofibers by single nozzle electrospinning

Highlights: • This is for the first time that, we have synthesized direct deposition of hollow IrO₂ nanofibers having average diameter of about ~45 nm on flexible stainless steel using electrospinning technique. • The nanofibers annealed at 400 °C, exhibits specific capacitance of about 705F/g at 1 mA/cm² with good rate capability and cyclic stability. • A novel symmetric IrO₂/IrO₂ supercapacitor with a high operating voltage of 2 V is built using LiClO₄-PVA gel electrolyte. The symmetric supercapacitor exhibits an energy density of 59 Wh/kg at a power density of 714 W/kg and an excellent cycling stability and power capability which can glow red LED. Herein, we have synthesized iridium oxide (IrO₂) nanofibers using electrospinning technique and optimization of annealing temperature is undertaken in order to obtain high quality IrO₂ nanofibers. The annealing temperature is varied as 200, 300, 400 and 500 °C. The synthesized material has hollow nanofibrous morphology with average diameter ~45 nm. The formed nanofibers are amorphous in nature. The X-ray Photoelectron Spectroscopy (XPS) result revealed that synthesized iridium is in +4 oxidation state. The electrochemical performance of IrO₂ electrodes showed 2 V potential window in three electrode system using 1 M Sodium sulphate (Na₂SO₄) aqueous electrolyte. The maximum specific capacitance is obtained for sample annealed at 400 °C (705F/g at 1 mA/cm²) which is due to the well-developed morphology with complete removal of polymer content. Moreover, a novel solid state symmetric IrO₂/IrO₂ supercapacitor with a high operating voltage of 2 V is built. The symmetric supercapacitor exhibits an energy density of 59 Wh/kg at a power density of 714 W/kg and an excellent cycling stability. These results demonstrate the potentialities of using IrO₂ for symmetric supercapacitor for building high energy and power density devices.