Hierarchical V₄C₃T_X@NiO-reduced graphene oxide heterostructure hydrogels and defective reduced graphene oxide hydrogels as free-standing anodes and cathodes for high-performance asymmetric supercapacitors

Asymmetric supercapacitors (ASCs) based on a battery-type anode and a capacitive-type cathode have been attracting extensive interest because of their high energy density. Herein, NiO nanosheets are hydrothermally deposited onto a V4C3TX substrate, which are then assembled into a 3D porous heterostructure hydrogel through a graphene oxide-assisted self-convergence hydrothermal process at low temperatures. The resultant hierarchical V4C3TX@NiO-RGO heterostructure hydrogel exhibits an ultrahigh specific capacitance of up to 1014.5 F g-1 at 1 A g-1. In addition, a defective reduced graphene oxide (DRGO) hydrogel is prepared using a cost-effective hydrothermal procedure followed by cobalt-catalyzed gasification, which shows a higher specific capacitance (258 F g-1 at 1 A g-1) than the untreated RGO hydrogel (176 F g-1). These two electrodes are then assembled into an ASC; the device features a stable operating voltage of 1.8 V, a maximum energy density of 86.22 W h kg-1 at 900 W kg-1, and excellent cycling stability at 96.4% capacitance retention after 10 000 cycles at 10 A g-1. The results from this work highlight the unique potential of MXene-based materials for the construction of high-performance ASCs.