Spontaneous three-dimensional self-assembly of MXene and graphene for impressive energy and rate performance pseudocapacitors

Abstract

Integration of pseudocapacitive nanomaterials within graphene based 3D-hydrogel network has shown suitable synergist in rate performance energy storage, but implementing the same with MXene through conventional heat involved processing is challenging due to its oxidation prone surface. Herein, we present a purely room temperature casting based approach to develop 3D-hydrogel hybrids of MXene and graphene (MGH) via metallic zinc particles induced spontaneous gelation, avoiding oxidation possibility. MGH was used as supercapacitor electrode that exhibits high mass specific capacitance of 357 F g–1 at 10 mV s–1, and excellent capacity retention of 95.6% after 10000 charge-discharge cycles. MGH was used as negative electrode to develop asymmetric supercapacitor, in combination with polyaniline (PANI)-graphene hybrid hydrogel (PGH) as positive electrode, that delivers a maximum energy density of 30.3 Wh kg–1 and a power density of 1.13 kW kg–1 with excellent capacity retention over 10000 cycles. In comparison to compact electrodes where pseudocapacitive materials cannot display their faradic activity with full potential, the hydrated porous network of MXene-graphene hydrogels with continuous channels permit the electrolyte ions to efficiently access MXene and PANI, thereby displaying high gravimetric and rate performance. MXene-graphene hydrogels, developed via this facile and cost effective protocol, are also attractive candidate for wide application areas that requires 3D porous structure.