A common method for making graphene is chemical vapor deposition on sheets of copper. When this happens there is the possibility for a layer of copper oxide to form between the copper and the graphene, and numerous graphene studies have noted this, but never looked too carefully at it. The Rice researchers almost did not look at it either, as they were just trying to make copper nanowires coated in carbon. Testing the wires gave some unexpected results because the copper oxide layer was still there. Closer examination showed it was acting as an insulator between the conductive graphene and copper, forming a capacitor. A good capacitor too as it breaks the records for other microcapacitors.
By connecting together millions of these nanocables, it should be possible to create a large-scale energy-storage device. Exactly how much energy such an array could store is hard to say at the moment, especially as quantum mechanics plays a role at the scale of a single nanocable. However, even if it is not able to challenge a conventional battery, it may still be able to transmit radio signals at the nanoscale, similar to the coaxial cables the give our televisions an image.