Reduced Graphene Oxide Hydrogels Deposited in Nickel Foam for Supercapacitor\nApplications: Toward High Volumetric Capacitance

Abstract

Graphene\nhydrogels have been considered as ideal materials for high-performance\nsupercapacitors. However, their low volumetric capacitance significantly\nlimits its real application. In this study, we report an environment-friendly\nand scalable method to prepare high packing density, electrochemically\nreduced graphene oxide hydrogels (ERGO) for supercapacitor application\nby the electrophoretic deposition of graphene oxide onto nickel foam,\nfollowed by the electrochemical reduction and hydraulic compression\nof the deposited materials. The as-prepared ERGO on nickel foam was\nhydraulic compressed up to 20 tons, resulting in an increase of the\npacking density of ERGO from 0.0098 to 1.32 g cm^–3. Consequently, the volumetric capacitance and volumetric energy\ndensity of ERGOs greatly increased from 1.58 F cm^–3 and 0.053 Wh cm^–3 (as-prepared ERGO) to 176.5\nF cm^–3 and 6.02 Wh cm^–3 (ERGO\ncompressed at 20 tons), respectively. The ERGOs also exhibited long-term\nelectrochemical stability with a capacitance retention in the range\nof approximately 79–90% after 10 000 cycles. We believe\nthat these high packing density ERGOs are promising for real-world\nenergy storage devices for which scalable, cost-effective manufacturing\nis of significance and for which space constraints are paramount.