Gate Field Induced Extraordinary Energy Storage in MoS₂-Graphene-Based Ultramicro-Electrochemical Capacitor

On-chip microscopic energy systems have revolutionized device design for miniaturized energy storage systems. Many atomically thin materials have provided a unique opportunity to develop highly efficient small-scale devices. We report an ultramicro-electrochemical capacitor with two-dimensional (2D) molybdenum disulphide (MoS 2 ) and graphene-based electrodes. Due to the tunable density of states, 2D MoS 2 provides electric field-induced doping and, combined with a graphene interface, leads to a high carrier mobility. The fabricated solid-state energy storage device is obtained using a gel electrolyte that provides an electrochemical capacitance of 1.8 mF/cm 2 . An extraordinary enhancement of ∼3000% in electrochemical capacitance (55 mF/cm 2 from 1.8 mF/cm 2, measured from a cyclic voltammetry curve) is observed upon application of back-gate field of −25 V, which is more than the enhancement (18%) observed in a MoS 2 electrochemical capacitor (0.95 mF/cm 2 from 0.8 mF/cm 2 ) without graphene, whereas the galvanic charge–discharge measurements analysis shows ∼1677% enhancement under the application of −25 V back-gate voltage. Thus, the electric field-induced doping in 2D MoS 2, in addition to a high charge carrier mobility due to the graphene, plays a crucial role in an extraordinary large energy storage in the ultramicro-electrochemical capacitor. We also evaluated the capacitance response using an AC signal superimposed with the DC bias to investigate the influence of polarization potential on the electrolyte. The study provides a benchmark development of an ultramicro-electrochemical capacitor for ultrahigh charge storage capability.