While graphene shows exciting promise as a next generation material for energy-storage applications such as lithium ion batteries and supercapacitors, a modified graphene-based structure is necessary to realize its full potential as an electrode material. Publishing their results in the journal Nanotechnology, researchers at Stevens Institute of Technology have fabricated a graphene-CNT hybrid structure in order to solve the current problem of self-aggregation of graphene flakes.

Controlled suppression of carbon etching

An out-of-plane, direct growth of CNTs on planar graphene was achieved via an APCVD process by controlling competing reactions of carbon formation and hydrogenation, which allow and repress CNT growth via hydrogen etching of carbon, respectively.

In this work, cyclic voltammetry results for the graphene-CNT hybrid structure exhibited larger capacitance (490.3 µF/cm2) than graphene-only electrodes (99.6 µF/cm2) at scan rates of 300 mV/s, indicating high rate performance.

Hybrid configuration

Because the CNTs were directly grown on planar graphene layers, the bulk of the exposed surface was used for electrical double layer (EDL) formation compared with the limited active surface area for EDL formation in chemically synthesized graphene-based electrode materials.

In the hybrid configuration both graphene and the CNT array serve as active materials for charge storage. In addition, the outstanding electrical properties of both materials ensure good electrical contact, a direct result of the direct growth of the CNTs on the graphene layer.

This work demonstrates the potential of graphene-CNTs hybrid structures for energy-storage applications and represents a milestone towards the group's ultimate goal of 3D multi-stack graphene structures for supercapacitor applications.

More details can be found in the journal Nanotechnology.