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 (MoS2) and graphene-based electrodes.
Due to the tunable density of states, 2D MoS2 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/cm2. An extraordinary
enhancement of ∼3000% in electrochemical capacitance (55 mF/cm2from 1.8 mF/cm2, 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 MoS2 electrochemical capacitor (0.95 mF/cm2 from 0.8
mF/cm2) 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 MoS2, 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.