High pseudocapacitance from ultrathin V₂O₅ films electrodeposited on self-standing carbon-nanofiber paper

An ultrathin V₂O₅ layer was electrodeposited by cyclic voltammetry on a self-standing carbon-nanofiber paper, which was obtained by stabilization and heat-treatment of an electrospun polyacrylonitrile (PAN)-based nanofiber paper. A very-high capacitance of 1308 F g^-1 was obtained in a 2 M KCl electrolyte when the contribution from the 3 nm thick vanadium oxide was considered alone, contributing to over 90% of the total capacitance (214 F g^-1) despite the low weight percentage of the V₂O₅ (15 wt%). The high capacitance of the V ₂O₅ is attributed to the large external surface area of the carbon nanofibers and the maximum number of active sites for the redox reaction of the ultrathin V₂O₅ layer. This ultrathin layer is almost completely accessible to the electrolyte and thus results in maximum utilization of the oxide (i.e., minimization of dead volume). This hypothesis was experimentally evaluated by testing V₂O₅ layers of different thicknesses. An ultrathin film of V₂O₅ is electrodeposited on the surface of carbon nanofibers to obtain a high surface area with an improved electrode conductivity. This provides a high pseudocapacitance of 1308 F g^-1 with respect to the effective contribution from the deposited oxide layer. The schematic shows the distribution of V₂O₅ throughout the nanofiber. The graph shows the dependence of the specific capacitance on the deposited amount of V₂O₅.