Anomalous Capacitive Behaviors of Graphene Oxide Based Solid-State Supercapacitors
Q Zhang and K Scrafford and MT Li and ZY Cao and ZH Xia and PM Ajayan and BQ Wei, NANO LETTERS, 14, 1938-1943 (2014).
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.
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