Supercapacitor Electrodes with Remarkable Specific Capacitance Converted from Hybrid Graphene Oxide/NaCl/Urea Films

A novel approach to improve the specific capacitance of reduced graphene oxide (rGO) films is reported. We combine the aqueous dispersion of liquid-crystalline GO incorporating salt and urea with a blade-coating technique to make hybrid films. After drying, stacked GO sheets mediated by solidified NaCl and urea are hydrothermally reduced, resulting in a nanoporous film consisting of rumpled <i>N</i>-doped rGO sheets. As a supercapacitor electrode, the film exhibits a high gravimetric specific capacitance of 425 F g<sup>–1</sup> and a record volumetric specific capacitance of 693 F cm<sup>–3</sup> at 1 A g<sup>–1</sup> in 1 M H<sub>2</sub>SO<sub>4</sub> aqueous electrolyte when integrated into a symmetric cell. When using Li<sub>2</sub>SO<sub>4</sub> aqueous electrolyte, which can extend the potential window to 1.6 V, the device exhibits high energy densities up to 35 Wh kg<sup>–1</sup>, and high power densities up to 10<sup>4</sup> W kg<sup>–1</sup>. This novel strategy to intercalate solidified chemicals into stacked GO sheets to functionalize them and prevent them from restacking provides a promising route toward supercapacitors with high specific capacitance and energy density.