Substantial differences in charge storage mechanisms exist between dielectric capacitors (DCs) and electrochemical capacitors (ECs), resulting in orders of magnitude difference of stored charge density in them. However, if ionic diffusion, the major charge transport mechanism in ECs, is confined within nanoscale dimensions, the Helmholtz layers and diffusion layers will overlap, resulting in dismissible ionic diffusion. An interesting contradiction between appreciable energy density and unrecognizable ionic diffusion is observed in solid-state capacitors made from reduced graphene oxide films that challenge the fundamental charge storage mechanisms proposed in such devices. A new capacitive model is proposed, which combines the two distinct charge storage mechanisms of DCs and ECs, to explain the contradiction, of high storage capacity yet undetectable ionic diffusion, seen in graphene oxide based supercapacitors.

This study demonstrates the microscale and nanoscale mechanical properties of a multiwalled carbon nanotubes/ polyether ether ketone (MWCNTs/PEEK) composite utilizing a novel in situ testing method. Nanoscale testing specimens of a composite of PEEK thin film dispersed with 6.5 wt% MWCNTs were successfully prepared using focused ion beam (FIB) and investigated by a tensile testing device accommodated inside a field emission scanning electron microscope. The average tensile strength of the nanocomposite was measured to be 388.66 MPa. The average Young's modulus measured at 6.52 GPa demonstrated a 23% increase compared to that of the bulk specimen, suggesting a sizedependent mechanism that limits the plastic deformation of the microscale specimens possibly due to the limited defects distribution and motion constraint of the polymer chain in the small specimen and the amorphous regions of the PEEK matrix.