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 N-doped rGO sheets. As a supercapacitor electrode, the film exhibits a high gravimetric specific capacitance of 425 F g^-1 and a record volumetric specific capacitance of 693 F cm^-3 at 1 A g^-1 in 1 M H₂SO₄ aqueous electrolyte when integrated into a symmetric cell. When using Li₂SO₄ aqueous electrolyte, which can extend the potential window to 1.6 V, the device exhibits high energy densities up to 35 Wh kg^-1, and high power densities up to 10⁴ W kg^-1. 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.