A 2D graphene-manganese oxide nanosheet hybrid synthesized by a single step liquid-phase co-exfoliation method for supercapacitor applications

The exfoliation of bulk-layered materials into 2D-nanosheets dramatically enhances their surface area and opens up novel properties. The exploitation of these advantageous properties for use in energy storage is, however, conditioned by the effective utilization of the available surface area and the effective combination of 2D-nanosheets holding complementary properties. In this work, a 2D graphene-manganese oxide nanosheet hybrid, in which graphene was interleaved between manganese oxide nanosheets, was synthesized following a novel single-step liquid-phase co-exfoliation method. This active material was used to manufacture supercapacitor electrodes using a scalable spray deposition method. The interleaving of graphene between manganese oxide nanosheets enabled a better use of the pseudocapacitive properties of the manganese oxide nanosheets (the hybrid was tested in a 0.5 M K2SO4 aqueous electrolyte) achieving a geometric capacitance of 80 mF cm−2 (single electrode), volumetric capacitances of 300 F cm−3 (single electrode) and 40.9 F cm−3 (symmetric device), and volumetric energy and power of 5.5 mWh cm−3 and 2,193.1 mW cm−3 (symmetric device), respectively. This performance is promising in the context of micro-supercapacitor applications, where performance per unit area and per unit volume are relevant for miniaturization. This work demonstrates the remarkable versatility of liquid-phase exfoliation to synthesize hybrids with tailored properties providing the proof-of-concept work for further investigation and exploitation of 2D hybrids for supercapacitor applications.