Energy storage has become a rapidly emerging and increasingly applied technology due to increasing electricity consumption by modern portable electronic devices and electric vehicles. In this respect, electrochemical supercapacitors have emerged as promising energy storage devices. Nano-hybrid materials benefiting from the synergy between the individual components and their unique features have been the pioneering materials in energy-storage field for fabricating high performance supercapacitors. [1] Specifically, composite structures of high power density carbon-based materials (e.g. graphene, carbon nanotubes, activated carbon, etc.) and high energy density transition metal oxides (e.g. RuO₂, MnO₂, Co₃O₄, NiO, Fe₂O₃, etc.) have been attractive electrode candidates. [2] Among the many transition-metal oxides, vanadium oxides are a particularly promising due to their high specific capacitance, wide potential window, earth-abundant nature and multiple oxidation states exhibited by vanadium (II-V). Integrating vanadium oxides with carbon-based materials is an effective strategy to enhance the poor electronic conductivity of vanadium oxide and increase the total surface area exhibited by individual components. As a commonly used carbon-based material, graphene has intriguing properties of high thermal and electronic conductivity, excellent mechanical strength, and high specific surface area.[3] By combining the merits of three-dimensional (3D) graphene networks and vanadium pentoxide (V₂O₅), composite electrodes exhibiting enhanced performances in energy density, power density, rate capability and cycling stability can be achieved.

In this work, we present a versatile, short one-step approach to prepare freestanding, macroscopic 3D networked V₂O₅/graphene aerogels. Cross-linker was used to facilitate the formation of the hybrid aerogels thorough chemical grafting to carbon in graphene oxide (GO) functional groups and to vanadium in V₂O₅. The cross-linker mediated self-assembly process allowed the homogenous distribution of V₂O₅ on graphene nanosheets. The resulting 3D composite aerogel forms a highly porous architecture of interconnected networks. Such transition metal oxide-graphene-based aerogels hold great promise in energy storage applications. When the resulting lightweight and porous V₂O₅-graphene aerogels were evaluated as supercapacitor electrodes, they were able to deliver a maximum energy density of 43.0 Wh kg^-1 at a power density of 0.48 kW kg^-1 at 0.6 A g^-1 and can hold 24.2 Wh kg^-1 at a maximum power density of 9.3 kW kg^-1 at 10 A g^-1. Moreover, this performance is much higher than the vanadium oxide-graphene aerogels prepared in the absence of the cross-linker. This was attributed to the efficient contact of the uniformly grown two-dimensional vanadium oxide nanoribbons on graphene layers in cross-linker mediated aerogels. The developed composites of V₂O₅ decorated graphene offer the following merits: they (i) facilitate diffusion of electrolyte ions by providing facile transfer pathways through the porous structure, (ii) offer high surface area, and thus rich surface redox reactions and (iii) offer conductive electron pathways for high rate capability. Moreover, the cross-linker mediated V₂O₅-graphene aerogels exhibit a long cycle life by retaining 80% of its initial capacitance after 10000 cycles.

References

[1] D. Dubal, O. Ayyad, V. Ruiz and P. Gómez-Romero, Chemical Society Reviews, 2015, 44, 1777-1790.

[2] G. Wang, L. Zhang and J. Zhang, Chemical Society Reviews, 2012, 41, 797-828.

[3] X. Huang, X. Qi, F. Boey and H. Zhang, Chemical Society Reviews, 2012, 41, 666-686.