  Nanosized energy storage, energy-harvesting, and functional devices are the
three key components for integrated self-power systems. Here, we report on
nanoscale electrochemical devices with a nearly three-fold enhanced stored
charge under the field effect. We demonstrated the field-effect transistor can
not only work as a functional component in nanodevices but also serve as an
amplifier for the nanosized energy storage blocks. This unusual increase in
energy storage is attributed to having a wide range of accessible electronic
density of states (EDOS), hence redox reactions are occurring within the
nanowire and not being confined to the surface. Initial results with MoS2
suggest that this field effect modulated energy storage mechanism may also
apply to many other redox-active materials. Our work demonstrates the novel
application of the field-effect in energy storage devices as a universal
strategy to improve ion diffusion and the surface-active ion concentration of
the active material, which can greatly enhance the charge storage ability of
nanoscale devices. The fabrication process of the field-effect energy storage
device is also compatible with microtechnology and can be integrated into other
microdevices and nanodevices.
