Free-standing composite hydrogel films for superior volumetric capacitance

High volumetric capacitance is vital for the development of wearable and portable energy storage devices. We herein introduce a novel simple route for the fabrication of a highly porous, binder-free and free-standing polyaniline/reduced graphene oxide composite hydrogel (PANi/graphene hydrogel) as an electrode with a packing density of 1.02 g cm-3. PANi played critical roles in gelation, which include reduction, crosslinking, creation of pseudocapacitance and as a spacer preventing graphene sheets from stacking. The composite hydrogel film delivered a volumetric capacitance of 225.42 F cm-3 with a two-electrode supercapacitor configuration, which was enhanced to 592.96 F cm-3 in a redox-active electrolyte containing hydroquinone. This new strategy will open a new area for using conducting polymer derivatives in the development of flexible graphene electrodes towards many applications such as batteries, sensors and catalysis.